Infants born with birth defects have poorer outcomes in terms of mortality and disability, but the long-term intellectual outcome in children with birth defects is generally unknown. We assessed the long-term associations of various birth defects with mortality and disability, and evaluated whether high mortality and disability were reflected in impaired intellectual performance at age 18. In this nationwide cohort study, records of 9,186 males with and 384,384 without birth defects, registered in the Medical Birth Registry of Norway (1967-1979) were linked to the National Conscript Service (1984-1999). Mortality and disability before military draft, and intelligence test score at conscription were the main outcome measures. Males with birth defects had a relative risk for disability of 6.0 compared with males without defects. Disability was low within categories of birth defects associated with low mortality, and high within defect categories associated with high mortality. The relative risk for not being drafted was highest if maternal educational level was low. Heart defects and cleft palate were the only subgroups in which intellectual performance was lower after adjustment for maternal education, maternal age, marital status and birth order. In particular, intellectual performance was not impaired among those with multiple compared with single defects. We conclude that for the majority of birth defect categories in the present birth cohort, our hypothesis that intellectual performance would be impaired was not confirmed. Thus, there seems to be little reason to fear an adverse intellectual outcome in non-disabled surviving infants with birth defects.