OBJECTIVE:To compare pregnancy outcomes between obese and nonobese women and to determine the effect of gestational weight gain on pregnancy outcome in obese women. METHODS: A retrospective cohort study was conducted comparing 100 obese and 300 nonobese women who delivered a singleton live birth at Yeungnam university hospital from June 1998 to Dec 1998. Morbid obesity was defined as a body mass index greater than 30. The incidence of selected perinatal and neonatal outcome was assessed for two groups. RESULTS: Morbidly obese patients were more likly to experience pregnancy complications including gestational diabetes mellitus, preeclampsia, placental abruption, fetal distress, meconium aspiration, cesarean delivery & birth trauma. However, these were not affected by gestational weight gain in morbidly obese women. Weight gains more than 12kg were strongly associated with birth of a large for gestational age(LGA) neonate, however, poor weight gain did not appear to incrcase the risk of delivery of a low birth weight neonate. CONCLUSION: To optimize fetal growth, weight gain of 7-12kg for obese women appear to be appropriate. To reduce the risk of delivery of an LGA neonate, the optimal gestational weight gain for obese women should not exceed 12kg.