The aim of this study is to assess whether intellectual ability in young adult men predicts the development of type 2 diabetes in later life. 641 men participating in the Helsinki Birth Cohort Study were administered a 2-h (75 g) oral glucose tolerance test at a mean age of 61 years. Intellectual ability was assessed during compulsory military service at a mean age of 20 years. Associations were explored using linear and logistic regression models. Intellectual ability in young adulthood did not predict glucose tolerance at age 61 years. However, educational attainment was associated with the prevalence of type 2 diabetes, independently of early intellectual ability. Men with the highest educational attainment were less likely to have type 2 diabetes than men with the lowest educational attainment (OR = 0.50, 95% CI 0.28-0.91). While education seems to protect from type 2 diabetes, we could not detect a connection between early intellectual ability and impairment in glucose regulation in later adulthood.