OBJECTIVES: The purpose of this study is to evaluate and compare the maternal and neonatal complications of the overt diabetes with that of gestational diabetes. METHOD : The medical records of 65 pregnant patients complicated by diabetes mellitus at Eulji medical center from January, 2001 to December, 2002 were reviewed retrospectively. Thirteen patients of them were diagnosed as a overt diabetes and the others were diagnosed as a gestational diabetes. RESULTS: Maternal complications were that preeclampsia in 15.4% and preterm labor in 15.4% in overt diabetes patients and preeclampsia in 9.6%, fourth degree laceration in 1.9%, preterm labor in 3.8%, placenta abruption in 1.9%, cardiomyopathy in 1.9% and polyhydroamnios in 1.9% in gestational diabetes patients. Neonatal complications were that hypoglycemia in 38.5% and respiratory distress syndrome in 15.4% in overt diabetes patients and hypoglycemia in 25%, hyperbilirubinemia in 9.6% and shoulder dystocia in 1.9% in gestational diabetes patients. There were no statistic differences in maternal and neonatal complications in two groups when management had done. And in gestational diabetes group, maternal and neonatal complications were significantly higher in no management group than management group regardless of management types. CONCLUSION: If early detection and management were done in overt and gestational diabetes, there were no difference in maternal and neonatal complications. Regardless of types of diabetes, early detection and management were important.