Thirty-six twin boys aged between nine and 13 were assessed for intelligence and reading disability. Records of their birth status, early language development and social demographic characteristics were also available. 72 per cent of the sample had an accuracy reading age below their chronological age, and 59 per cent had a comprehension reading age below their chronological age, despite above-normal IQ. The best predictor of reading disability was preschool language status, accounting for 33 per cent of the variance in accuracy reading age discrepancy, and 23 per cent in comprehension reading age discrepancy in regression equations. This study shows that male twins are at very high risk for reading disability, and also offers support for the claim that language disability is basic to the development of reading problems.