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The International Dyslexia Association (IDA) adopted a revised definition of dyslexia on October 22, 2025, updating its widely referenced 2002 working definition. The new wording describes difficulties with word reading and/or spelling, recognizes that their form can vary across writing systems, and treats dyslexia as arising from interacting influences rather than one universal cause.
What is the IDA’s new definition of dyslexia?
The IDA’s 2025 definition reads:
“Dyslexia is a specific learning disability characterized by difficulties in word reading and/or spelling that involve accuracy, speed, or both and vary depending on the orthography. These difficulties occur along a continuum of severity and persist even with instruction that is effective for the individual’s peers. The causes of dyslexia are complex and involve combinations of genetic, neurobiological, and environmental influences that interact throughout development. Underlying difficulties with phonological and morphological processing are common but not universal, and early oral language weaknesses often foreshadow literacy challenges. Secondary consequences include reading comprehension problems and reduced reading and writing experience that can impede growth in language, knowledge, written expression, and overall academic achievement. Psychological well-being and employment opportunities also may be affected. Although identification and targeted instruction are important at any age, language and literacy support before and during the early years of education is particularly effective.”
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The definition is about dyslexia as a specific learning disability, not a single reading profile that every person must share. The IDA’s definition page gives the adoption date and full wording.
What changed from the 2002 definition?
The earlier IDA definition, adopted November 12, 2002, centered on difficulties with accurate and/or fluent word recognition, spelling, and decoding, and said these were typically linked to a deficit in the phonological component of language. The 2025 wording keeps reading and spelling at its center but expands how it describes the difficulties, their causes, and their possible consequences. The IDA calls the revision its first major update since the widely referenced 2002 working definition; the interval was almost 23 years, so “in 20 years” is a rounded headline rather than an exact count.
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| Aspect | 2002 IDA wording | 2025 IDA wording |
|---|---|---|
| Core difficulty | Accurate and/or fluent word recognition, spelling, and decoding. | Word reading and/or spelling difficulties involving accuracy, speed, or both. |
| Writing systems | The archived wording does not describe variation by orthography. | States that difficulties vary depending on orthography—the writing system. |
| Severity and persistence | The archived wording does not use the new continuum-and-persistence formulation. | Describes a continuum of severity and difficulties that persist even with instruction effective for an individual’s peers. |
| Contributing factors | Typically linked the difficulty to a deficit in the phonological component of language. | Describes interacting genetic, neurobiological, and environmental influences; phonological and morphological difficulties are common but not universal. |
| Possible consequences | Included possible effects on reading comprehension and reduced reading experience. | Also names possible effects on writing experience, language and knowledge growth, written expression, academic achievement, psychological well-being, and employment opportunities. |
The archived 2002 definition and consensus history provides the earlier wording; the IDA’s explanation of the 2025 definition discusses the revision’s terms.
What does the new wording mean in practice?
Reading and spelling difficulties can look different
The definition identifies word reading and/or spelling as the central areas of difficulty and specifies accuracy, speed, or both. “Orthography” means the conventions and structure of a writing system. By noting that difficulties vary by orthography, the definition avoids treating the way dyslexia appears in one writing system as the only pattern. It does not set out a separate checklist for each language.
Severity is a continuum, and persistence matters
The definition does not frame dyslexia as an all-or-nothing category of difficulty. It says difficulties occur along a continuum and persist even with instruction that is effective for the individual’s peers. The IDA explains persistence as a way to distinguish dyslexia-related difficulties from transient challenges and discusses observing responses to supplemental instruction. That wording does not make any one response-to-intervention procedure the sole diagnostic test.
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There is no single stated cause or universal processing profile
The definition describes combinations of genetic, neurobiological, and environmental influences interacting through development; it does not say that environment alone causes dyslexia. It also says difficulties with phonological processing (working with speech sounds) and morphological processing (the meaningful parts of words) are common, but not universal. Early oral-language weaknesses can foreshadow literacy challenges, but the definition does not make them a requirement for dyslexia.
Possible effects can extend beyond reading
Reading comprehension problems and reduced reading or writing experience can affect opportunities to build language and knowledge, develop written expression, and achieve academically. The definition also says psychological well-being and employment opportunities may be affected. These are possible secondary consequences, not inevitable outcomes for every person with dyslexia.
What does the definition say about support?
The IDA states: “Although identification and targeted instruction are important at any age, language and literacy support before and during the early years of education is particularly effective.” Early support is emphasized, but the wording does not say that support later in life is ineffective. The definition itself describes broad principles; it is not an individual assessment or a detailed instructional plan.
The IDA’s explanation page discusses the wording, and its glossary and resource directory offers related resources.
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A 2026 peer-reviewed account by Hugh W. Catts, Charles W. Haynes, and R. Malatesha Joshi describes an iterative, data-driven review initiated by the IDA. The process included an 18-member Steering Committee and a 74-member Advisory Committee formed in April 2024, review of survey responses and relevant research, and a draft released for public comment in August 2025. The authors report that more than 3,000 public-comment responses were received and systematically reviewed; the count refers to responses, not necessarily unique people. The revised definition was approved in October 2025. The account is available in the peer-reviewed paper.
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