There is growing evidence that childhood IQ is inversely associated with mortality in later life. However, the specificity of this association in terms of causes of death, whether it is continuous over the whole range of IQ scores and whether it is the same according to age and sex is not clear. In a large cohort (N = 11,603) of a complete population of children born in one city in the UK in the early 1950s, IQ measured at age 7 years (using a routinely administered picture test) was found to be inversely associated with mortality between the ages of 15 and 57 years. For every 1 SD increase in IQ at 7, the all cause mortality hazard ratio was 0.79 (95% CI 0.73, 0.85). On adjustment for a range of perinatal factors, father's social class at birth, number of sibs in the household and childhood height and weight, this was attenuated slightly to 0.81 (0.74, 0.88). Almost identical associations of IQ with mortality were seen for men and women as well as at younger (15-39) and older (40+) ages. These associations were across the entire IQ range, although some of the high mortality in the lowest category of IQ (less than 70) was accounted for by causes associated with congenital disorders. Overall, external causes of death showed the strongest association, with weaker associations being seen for cancer. Further work is required to understand the mechanisms whereby childhood IQ has such a robust association with mortality in later life. (Contains 6 tables.)