BackgroundThe association between childhood cognitive ability measured with IQ tests and mortality is well documented. However, studies on the association in women are few and conflicting, and the mechanisms underlying the association are unclear.MethodsData on IQ were collected at school at age 13 among 19 919 men and women born in 1948 and 1953. Information on childhood socioeconomic position, the participants' socioeconomic and social circumstances in middle age and mortality up to 2013 was collected through national registers.ResultsLower IQ was associated with an increased risk of all-cause mortality among men (1070 cases, HR 1.31, 95% CI 1.23 to 1.39 for one SD decrease in IQ) and among women (703 cases, HR 1.16, 95%CI 1.08 to 1.25). IQ was associated with mortality from several causes of death in men, and cancer and cardiovascular disorder mortality in women. Adjustment for socioeconomic factors in childhood and, in particular, in adulthood attenuated the associations considerably in men and near completely in women.ConclusionLower IQ was associated with an increased risk of mortality in men and women. The explanatory effects of socioeconomic factors in adulthood suggest that they constitute an important pathway in the association between IQ and mortality, especially in women.