The in utero environment is a powerful risk factor for type 2 diabetes in offspring, but little is known about the risk conveyed by nondiabetic gestational glucose levels. This issue was explored in 911 nondiabetic Pima Indian mothers and 1,436 of their children. Associations were assessed in multivariate models between maternal third trimester glucose tolerance and indexes of body composition and glycemic control in their children. At parturition, the mothers' ages ranged from 14 to 43 years. Offspring were studied at age 0-39 years. An SD (1.3 mmol/l) of maternal glucose was associated with 56 g higher birth weight (P = 0.0002). This effect persisted when only offspring of normal glucose tolerant mothers were examined (57 g, P < 0.0001). In Cox proportional hazards models, the adjusted hazard rate ratio for offspring risk of diabetes per SD maternal glucose was 1.6 (95% CI 1.3-2.0, P < 0.0001). When only offspring of normal glucose tolerant mothers were examined, the risk was reduced but remained significant (1.3 [1.04-1.71], P = 0.026). In conclusion, maternal glycemia during pregnancy is associated with increased birth weight and risk of diabetes in Pima Indian offspring, even when mothers are normal glucose tolerant during pregnancy. Thus, prevention of offspring type 2 diabetes may require strategies that focus on improving gestational glucose tolerance even within the normal range.