The present study was performed to evaluate pregnancy outcomes in women with type 1 and type 2 diabetes mellitus (DM) in Japan. This multi-institutional retrospective study was conducted in 40 general hospitals in Japan during 2003-2009. We evaluated 369 and 579 pregnant women with type 1 and type 2 DM, respectively, and compared pregnancy outcomes between the two groups. Glycosylated hemoglobin levels in the first trimester did not differ significantly between the studied groups. Gestational weight gain was lower in type 2 DM than in type 1 DM. Although there were no significant differences in perinatal outcomes between the groups, the primary cesarean section rate was higher in type 2 DM than in type 1 DM. Multiple logistic regression analysis revealed that primigravida status, pre-gestational body mass index (BMI), gestational weight gain, chronic hypertension, and microvascular disease including diabetic retinopathy or nephropathy were associated with onset of pregnancy-induced hypertension. Further, pre-gestational BMI was associated with the need for primary cesarean section. This study demonstrated that no differences were observed in the rates of perinatal mortality and congenital malformation between pregnant women with type 1 DM and type 2 DM; however, women with type 2 DM displayed a higher risk of primary cesarean section.