Patients with insulin-dependent diabetes are prone to infection, possibly related to poor metabolic control. Relative immune deficiency exists in pregnancy. We hypothesized that pregnant patients with insulin-dependent diabetes are at an increased risk for infection and that infection is related to poor glycemic control. We matched 65 pregnant women with insulin-dependent diabetes to 65 nondiabetic pregnant controls. At least one episode of infection before delivery occurred in 83% of the women with insulin-dependent diabetes (26% in control group). The rate of postpartum infection was five times higher in the group with insulin-dependent diabetes and they were susceptible to more kinds of infections. Although there was no overall difference among the indices of glycemic control, hemoglobin A1 obtained before the infection was higher than during infection. We conclude that a high rate of infection exists in pregnant women with diabetes; infection and poor glycemic control may be associated, but it is unclear whether improvement in metabolic control will reduce this high infection rate.