The influence of childhood socioeconomic status (SES) on incidence of type 2 diabetes mellitus has not previously been studied. The authors prospectively examined the association of childhood SES (father's occupation) with incidence of diabetes in 100,330 US women who were followed from 1980 to 2002. In 55,115 of those women, 10-year follow-up data (1992-2002) were also available on adult SES (spouse's education). In all, 6,916 new cases of type 2 diabetes were documented. Compared with women from white-collar occupational backgrounds, the multivariate-adjusted risks of diabetes were 1.08 (95% confidence interval (CI): 0.95, 1.23) among women whose fathers were laborers and 1.10 (95% CI: 1.03, 1.16) among women whose fathers were blue-collar or lower white-collar workers. Lower adult SES was associated with risk of diabetes independently of childhood SES. Compared with women whose spouses had graduate degrees, women whose spouses were high school graduates had a 1.16 times higher risk of incident diabetes (95% CI: 1.04, 1.29), while women whose spouses had college degrees were at 1.14 times the risk (95% CI: 1.01, 1.29). Compared with women with stable high SES from childhood to adulthood, women with declining SES had a 1.18 times higher risk of incident diabetes (95% CI: 1.06, 1.32). Higher body mass index among women with lower SES accounted for much of these rather modest associations between childhood and adult SES and risk of diabetes.