This study was carried out to assess the prevalence of diabetes in southern Indian women during pregnancy. Nine hundred and fifty women having > or = 24 weeks of gestation, attending two general gynaecology centres for antenatal check-ups were screened. Initially, the screening test with 1-h plasma glucose sampling following 50 g glucose load was done and those with glucose values > or = 140 mg/dl were subjected to a 3-h oral glucose tolerance test (OGTT) with 100 g glucose load. Among the 950 women, 6 were known diabetic subjects. Of the other 944, 89 were positive on screening test and 67 of them reported for OGTT. Four were detected to have gestational diabetes mellitus (GDM) (O'Sullivan and Mahan's criteria). Therefore the prevalences of total diabetes and GDM were 1.19% and 0.56%, respectively.