Objective : To evaluate the clinical manifestations and perinatal outcomes of pregnancies complicated with gestational impaired glucose tolerance (GIGT) and gestational diabetes mellitus (GDM). Methods : We performed 50gm oral glucose tolerance test (OGTT) for GIGT and GDM screening in 4,367 pregnant women at 24-28 weeks of gestation. In 1,010 women with plasma glucose level over 130mg/dl, 753 women underwent 100gm OGTTs at 28-32 weeks of gestation. According to the NDDG criteria, 113 cases with GIGT (single positive level of OGTT ; group 2), 125 cases with GDM (group 3), and 515 cases with control (group 1) were identified among the 753 cases. Retrospective review of outcome of these patients was performed. ANOVA and chi-square test were used to determine the statistical significance. Results : The incidence of GIGT and GDM was 2.7%, 3.0%. The prepregnant body mass index (21.4±3.0kg/m2, 21.3±2.8kg/m2, 23.2±4.1kg/m2), overweight of BMI over 26 (7.4%, 4.4%, 14.4%) and obesity of BMI over 30 (1.2%, 0.0%, 8.0%) was significantly higher in group 3 than group 1 (p<0.05). We defined poor maternal outcome as those suffering from any one of birth canal injury, hydramnios or oligohydramnios, preeclampsia, cesarean delivery due to cephalopelvic disproportion, dystocia, fetal distress. Group 3 showed most highest poor maternal outcome (22.3%, 28.3%, 39.2%, p<0.05). And we defined poor neonatal outcome as those suffering from any one of hyperbilirubinemia, hypoglycemia, congenital anomaly, admission to neonatal intensive care unit due to respiratory distress syndrome. Group 2 and group 3 showed poor neonatal outcome than group 1 (6.2%, 13.3%, 21.6%, p<0.05). Conclusion : Pregnancies complicated with GDM showed poor maternal and neonatal outcome, and GIGT experienced no adverse maternal outcomes but showed poor neonatal outcomes compared to normal pregnancy, and showed less correlation with obesity than GDM. Further study of pathophysiology and proper management of GIGT will be mandatory.