Dyslexia in adults: what the definitions say
8 minute read · updated October 28, 2026
12 sources: 4 government or law, 2 peer-reviewed research, 6 charity or professional body
Major organizations describe dyslexia as a persistent difficulty with word reading and spelling, often showing up in adults as slow reading and spelling errors.[1] Definitions differ between the United States and the UK, and both were revised in 2025.[2][3] Reading difficulty itself has many possible causes, so a definition is not a test.
This page explains how dyslexia is defined by the organizations that most often shape assessment practice, and how those definitions describe adults. It does not describe signs to look for, and nothing here can tell you whether dyslexia applies to you. See what this site cannot do.
What the main definitions say
There is no single worldwide definition of dyslexia. A 2025 review by UK researchers notes that there have been many definitions over the past century and that debate about how to define it continues.[1] This page compares the International Dyslexia Association (IDA) definitions from the United States with two UK definitions: the 2009 Rose definition, long used in UK education, and the 2025 Delphi definition that the British Dyslexia Association has adopted.[1][3]
The International Dyslexia Association
IDA's 2002 definition described dyslexia as a specific learning disability that is neurobiological in origin, characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and decoding abilities, which typically result from a deficit in the phonological component of language (the sound structure of words).[1] It described these difficulties as often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction, with possible secondary effects on reading comprehension, vocabulary, and background knowledge.[1]
In 2025, IDA released a revised definition, its first update since 2002.[4] According to a question-and-answer guide from the National Center on Improving Literacy, the revision keeps dyslexia as a difficulty in word reading and/or spelling, says those difficulties may involve accuracy, speed, or both depending on the writing system, and describes dyslexia as arising from multiple interacting genetic, neurobiological, and environmental influences.[2] The same guide says the revised definition lists a wider range of secondary consequences, including effects on written expression, academic achievement, psychological well-being, and employment opportunities.[2]
The UK Delphi definition
The UK definition comes from a Delphi study, a method in which experts rate statements over several rounds until they agree. The panel of 58 included academics, specialist teachers, educational psychologists, and people with dyslexia, and it accepted 42 consensus statements.[1] Its proposed definition begins: "Dyslexia is a set of processing difficulties that affect the acquisition of reading and spelling."[1]
The Delphi definition also says that difficulties exist on a continuum of severity, that reading fluency and spelling difficulties are a key marker across languages and age groups, and that the nature and course of dyslexia depend on multiple genetic and environmental influences.[1] The British Dyslexia Association (BDA) said in February 2025 that it would adopt this definition, and that there is no suggestion that anyone diagnosed under the previous definition would stop meeting the criteria.[3]
| Point | IDA 2002 | IDA 2025 | UK Rose 2009 | UK Delphi 2025 |
|---|---|---|---|---|
| Core difficulty | Accurate and/or fluent word recognition, spelling, decoding[1] | Word reading and/or spelling, accuracy or speed or both[2] | Accurate and fluent word reading and spelling[1] | Processing difficulties affecting reading and spelling; fluency and spelling as key marker[1] |
| Causes named | Neurobiological in origin; phonological deficit[1] | Interacting genetic, neurobiological, environmental influences[2] | Not stated as cause; lists phonological awareness, verbal memory, verbal processing speed[1] | Multiple genetic and environmental influences[1] |
| Continuum of severity | Not highlighted[1] | Yes[2] | Yes[1] | Yes[1] |
| Co-occurring difficulties | Not mentioned[1] | Not covered in the NCIL guide | Mentioned[1] | Mentioned[1] |
Clinical manuals use different terms again. The American Psychiatric Association's DSM-5 uses the term "specific learning disorder in reading," and the World Health Organization's ICD-11 uses "developmental learning disorder with impairment in reading."[1] The Delphi authors note that ICD-11 requires reading to be below expectations for age and intellectual ability, while DSM-5 moves away from comparing intellectual ability with reading attainment.[1]
How dyslexia is described in adults
The Delphi panel agreed that while some older children and adults with dyslexia continue to have word-level reading problems, others mainly have difficulties with reading and writing fluency and with spelling.[1] The authors write that this implies dyslexia can be present even when some reading and spelling scores are in the average range, a view they describe as increasingly accepted when assessing adults and people who have had extensive support.[1]
The panel also agreed that the way dyslexia shows up can change over time depending on context, and that after intervention and support, reading may no longer be experienced as disabling even if it remains challenging.[1] The companion paper on assessment adds that in adults, difficulties may become more noticeable as the pace and demands of work increase, or when strategies a person has relied on become too difficult or tiring to keep up.[5]
The NHS states that dyslexia does not affect intelligence.[6] The Delphi panel agreed that a gap between intellectual ability and literacy attainment can be a useful indicator but is not sufficient for a diagnosis on its own.[1]
Across languages and backgrounds
Dyslexia is described in many languages, and the way it shows up depends on how a language is written.[1] The NCIL guide explains that in languages with very regular spelling, such as Spanish, Finnish, or Italian, reading accuracy often develops fairly quickly and difficulties may be most visible in reading speed, while in English and Danish difficulties often appear in both accuracy and speed.[2]
The same guide says that environmental conditions and dyslexia are not mutually exclusive: a person can have dyslexia and also have experienced poverty, interrupted schooling, limited access to books, or learning in more than one language.[2] It calls for assessment that does not exclude children from poverty or children learning English as an additional language.[2] In England, research cited in the 2025 assessment paper found that children in more deprived areas were less likely than children in more affluent areas to be identified with specific learning difficulties.[5]
Conditions that can occur alongside dyslexia
The Delphi panel strongly supported a neutral statement that dyslexia frequently co-occurs with one or more other developmental difficulties. The examples it names are developmental language disorder, ADHD, developmental coordination disorder, and dyscalculia (the panel's terms).[1] The BDA lists the same examples.[7] The authors add that more research is needed to understand why these conditions so often occur together.[1]
Some experiences are often linked with dyslexia but are separate from it. The Delphi panel agreed that visual stress, a sensitivity to high-contrast patterns such as lines of black text on white, is a separate condition from dyslexia, although it can make text harder to process.[1] The panel also distinguished developmental dyslexia from acquired dyslexia, which follows a brain injury or other neurological cause.[1]
UK assessment guidance from the SpLD Assessment Standards Committee (SASC) says specific learning difficulties can co-exist with overlapping conditions, and that assessors should refer a person to another practitioner when that is needed.[8]
Reading difficulty has many possible causes
Finding reading hard is an experience, not a diagnosis. The Delphi definition describes dyslexia as literacy attainment that is weak in relation to age, standard teaching, and other attainments, which means the quality of teaching a person received is part of the picture.[1] The NCIL guide puts it directly: not every person who finds reading difficult should be considered dyslexic, and identification has to be interpreted within the person's instructional and developmental context.[2]
Professional guidance lists several other things to consider. The NHS says a GP can check for conditions such as hearing problems and may suggest an eye test.[6] SPELD NSW in Australia advises checking eyesight and hearing before seeking a dyslexia assessment.[9] The SASC report format asks assessors to record vision (including a recent sight test), hearing, language history, consistent access to schooling, attendance, and the number of schools attended.[8]
The same format asks assessors to note test conditions, including the person's health, attention, anxiety, and fatigue on the day, because these can affect performance.[8] It also says that learning English as an additional language, or a complex language history, could help explain a pattern of results.[8]
Why some adults were not identified as children
The BDA notes that some people only discover they are dyslexic in adulthood, and suggests that misconceptions about dyslexia may be part of the reason.[10] The Delphi panel agreed that in older children and adults, early and persisting literacy difficulties may have been missed or masked, and that assessors should look into these histories.[5]
Rules for who qualified for help have also changed. In 2011, the US National Institute of Child Health and Human Development (NICHD) reported that many school systems used a discrepancy model, comparing reading ability with IQ scores, to decide who received specialized reading instruction, so children with dyslexia and lower IQ scores might not qualify.[11] The study it described called that model into question.[11]
Access to assessment has also been uneven. The 2025 assessment paper cites a study of parents in which inadequate teacher training and insufficient school funding were seen as barriers to diagnosis, and describes provision in England as a "postcode lottery," where support depends on where a family lives.[5]
Where to read next
- Self-reflection, screening, and assessment explains what each can and cannot tell you.
- What a professional assessment may involve covers who carries out assessments in several countries.
- Searching for an online dyslexia test explains how to read the claims of online quizzes.
Review status
Source-checked, not expert-reviewed
Drafted with AI assistance. Each factual claim was checked against the source it links to on 2026-10-28. No clinician, psychologist or dyslexia specialist has reviewed this page. See the claims register.
Sources
- [1]Toward a consensus on dyslexia: findings from a Delphi study. Carroll, Holden, Kirby, Thompson, Snowling and the Dyslexia Delphi Panel. Journal of Child Psychology and Psychiatry (doi:10.1111/jcpp.14123), 2025. Accessed 2026-10-28. Peer-reviewed research
- [2]Explaining IDA's new definition of dyslexia: questions and answers (Reading the Room discussion series). National Center on Improving Literacy (developed under a US Department of Education grant), 2026. Accessed 2026-10-28. Government or law
- [3]Dyslexia Delphi study papers have now been finalised. British Dyslexia Association, 2025. Accessed 2026-10-28. Charity or professional body
- [4]IDA's new definition of dyslexia. LD@school (Learning Disabilities Association of Ontario), 2025. Accessed 2026-10-28. Charity or professional body
- [5]Towards a consensus for dyslexia practice: findings of a Delphi study on assessment and identification. Holden, Kirby, Snowling, Thompson and Carroll. Dyslexia 31(1): e1800 (doi:10.1002/dys.1800), 2025. Accessed 2026-10-28. Peer-reviewed research
- [6]Dyslexia. NHS (England). Accessed 2026-10-28. Government or law
- [7]What is dyslexia?. British Dyslexia Association. Accessed 2026-10-28. Charity or professional body
- [8]Diagnostic Assessment Report for Specific Learning Difficulties (report format, no comments version). SpLD Assessment Standards Committee (SASC), 2025. Accessed 2026-10-28. Charity or professional body
- [9]Identification of specific learning difficulties. SPELD NSW. Accessed 2026-10-28. Charity or professional body
- [10]Am I dyslexic?. British Dyslexia Association. Accessed 2026-10-28. Charity or professional body
- [11]NIH-funded study finds dyslexia not tied to IQ (news release). NICHD, 2011. Accessed 2026-10-28. Government or law
- [12]Testing accommodations. US Department of Justice, Civil Rights Division (ADA.gov). Accessed 2026-10-28. Government or law
Related reading
- Self-reflection, screening, and assessment are different thingsWhy a reading questionnaire, a dyslexia screener, and a diagnostic assessment answer different questions, and why only the last can identify dyslexia.
- What a professional dyslexia assessment may involveWhat adult dyslexia assessments usually include, who carries them out in the US, UK, Ireland, Canada and Australia, and what to ask an assessor first.
- Searching for an online dyslexia testWhat online dyslexia quizzes and screeners can and cannot tell you, how to judge their claims, and what to check about your data before you answer.