Obstetric outcome in early onset and late onset GDM was compared in a prospective study conducted at the Department of Obstetrics & Gynecology in BIRDEM, Dhaka, Bangladesh. A total 120 pregnant women were recruited purposively for the study in which 60 were early onset GDM and 60 were late onset GDM during study period of January 2008 to December 2009. Patients were followed up in different periods of gestation, during delivery and early postpartum period & findings were compared between two groups. BMI & family history of diabetes were significantly higher in early GDM group (p<0.05). Evidence of increased glycaemia was observed in early GDM group & difference of glycaemic status was statistically significant (p<0.05). Insulin was needed in 85% of early onset GDM and 55% in late onset GDM. There was also significant difference (p<0.05). In this study, 23.3% of early onset GDM group developed pre-eclampsia while in late onset GDM it was 10% and was statistically significant (p<0.05). Regarding intrapartum & postpartum complications - perineal tear, PPH wound infection, puerperal sepsis were more in early onset than late onset GDM group with no significant difference. Regarding foetal outcome, 8.3% early GDM group delivered asphyxiated baby in comparison to 3.3% in late GDM group. Twenty percent (20%) of early onset GDM group had to admit their babies in neonatal unit while in late onset group it was 5%. There was significant difference between two groups (p<0.05). Neonatal hypoglycaemia was also statistically significantly (p<0.05) higher in early GDM group. Neonatal hyper-bilirubinaemia, RDS, perinatal death was more in early onset GDM subjects. Early onset GDM subjects are high risk subgroup & have significant deleterious effect on maternal and perinatal outcome than late GDM groups.