OBJECTIVE: We previously reported that people prenatally exposed to famine during the Dutch Hunger Winter of 1944-1945 have higher 2-h glucose concentrations after an oral glucose tolerance test in later life. We aimed to determine whether this association is mediated through alterations in insulin secretion, insulin sensitivity, or a combination of both. RESEARCH DESIGN AND METHODS: We performed a 15-sample intravenous glucose tolerance test in a subsample of 94 normoglycemic men and women from the Dutch Famine Birth Cohort. We used the disposition index, derived as the product of insulin sensitivity and the first-phase insulin response to glucose as a measure of the activity of the beta-cells adjusted for insulin resistance. In all analyses, we adjusted for sex and BMI. RESULTS: Glucose tolerance was impaired in people who had been prenatally exposed to famine compared with people unexposed to famine (difference in intravenous glucose tolerance test K(g) value -21% [95% CI -41 to -4]). People exposed to famine during midgestation had a significantly lower disposition index (-53% [-126 to -3]) compared with people unexposed to famine. Prenatal exposure to famine during early gestation was also associated with a lower disposition index, but this difference did not reach statistical significance. CONCLUSIONS: Impaired glucose tolerance after exposure to famine during mid-gestation and early gestation seems to be mediated through an insulin secretion defect