The International Dyslexia Association adopted the following definition of dyslexia on November 12, 2002:
Dyslexia is a specific learning disability that is neurological in origin. It is characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and decoding abilities. These difficulties typically result from a deficit in the phonological component of language that is often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction. Secondary consequences may include problems in reading comprehension and reduced reading experience that can impede the growth of vocabulary and background knowledge.
This definition has been adopted by the National Institute of Child Health and Human Development (NICHD) for its research programs in dyslexia and learning disabilities.