OBJECTIVE: To identify the early life predictors of childhood intelligence. DESIGN: Cohort study of 10 424 children who were born in Aberdeen (Scotland) between 1950 and 1956. RESULTS: Social class of father around the time of birth, gravidity, maternal age, maternal physical condition, whether the child was born outside of marriage, prematurity, intrauterine growth, and childhood height were all independently associated with childhood intelligence at ages 7, 9, and 11. The effect of social class at birth was particularly pronounced, with a graded linear association across the distribution even with adjustment for all other covariates (p<0.001 for linear trend). Those from the lowest social class (V) had intelligence scores that were on average 0.9-1.0 of a standard deviation lower than those from the higher groups (I and II) at each of the three ages of intelligence testing. Collectively, the early life predictors that were examined explained 16% of the variation in intelligence at each age. CONCLUSIONS: Father's social class around the time of birth was an important predictor of childhood intelligence, even after adjustment for maternal characteristics and perinatal and childhood factors. Studies of the association of childhood intelligence with future adult disease need to ensure that the association is not fully explained by socioeconomic position.