To describe maternal complications and neonatal outcomes caused by gestational diabetes mellitus a descriptive observational study was conducted in the department of obstetrics and gynaecology at Ramakrishna Mission Seva Pratisthan and Vivekananda Institute of Medical Sciences, Kolkata, over a period of one year from July 2009 to June 2010. Women diagnosed by oral glucose tolerance test as gestational diabetes mellitus were enrolled as study subjects and were followed regularly at outpatient department. Blood glucose levels controlled by diet or with insulin. Foetal well-being was assessed by ultrasonography, foetal kick count and cardiotocography. Time and mode of delivery were decided on admission depending upon the complications encountered. Intrapartum blood glucose level was monitored and foetal monitoring was done. After delivery all the babies were assessed by the paediatrician. After discharge patients were advised oral glucose tolerance test at 6 weeks postpartum. Out of 644 women delivered, 58 (9%) were diagnosed gestational diabetes mellitus and were studied. Mean age was 30 years and 55.2% were multigravida; 50% were obese (BMI > or = 30 kg/m2); 60.3% required insulin therapy to achieve glycaemic control. Most common maternal and neonatal complications observed were premature prelabour rupture of membrane (10.3%) and jaundice (29.3%) respectively. Caesarean section was done in 60.3% gestational diabetas mellitus mothers. A total of 57 babies (98.2%) were delivered alive.