BACKGROUND: Manifestations of dyslexia depend on language systems and scripts. This study explored the prevalence and clinical features of developmental dyslexia among monolingual Persian students and provided insights on mechanisms involved in reading Persian. METHODS: To measure reading ability we developed a new instrument, Analysis of Persian Reading Ability, which had acceptable validity and reliability. A total of 1562 children aged 6 ½ - 14 were randomly selected from a population of 109696 primary school students in the city of Qom, Iran. RESULTS: Using a variety of statistical and clinical criteria, 82 (5.2%) of the sample were classified as dyslexics. A detailed analysis of reading errors revealed eight types of errors related to three categories. The most frequent category in both dyslexic and the matched control group was phonological, followed by pragmatic and visual errors. CONCLUSION: The observed prevalence rate of dyslexia and reading error categories would suggest that Persian in vowel-free format is an opaque language and predominant use of a sub-lexical strategy is involved when reading Persian.