Reading achievement, as measured by individually administered standardized tests of reading accuracy or comprehension, is substantially below that expected given the person's chronological age, measured intelligence, and age-appropriate education.
The disturbance in the first criterion significantly interferes with academic achievement or activities of daily living that require reading skills.
If a sensory deficit is present, the reading difficulties are in excess of those usually associated with it.
Criteria summarized from:
American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders, fourth edition. Washington, DC: American Psychiatric Association.