BACKGROUND This study investigated postpartum metabolic abnormality in women with previous gestational diabetes mellitus (GDM) and predictive factors for postpartum glucose intolerance. METHODS From March 2001 to February 2003, 127 prior-GDM women underwent a 75g oral glucose tolerance test (OGTT) and metabolic assessment at least six weeks after delivery. To identify the predictors, clinical variables obtained at the time of GDM were compared. RESULTS The cumulative incidence rates of diabetes mellitus (DM) and abnormal glucose tolerance (AGT) i.e. impaired fasting glucose or impaired glucose tolerance, in women with previous GDM were 13.4% and 29.1%, respectively. Postpartum body mass index (BMI), total cholesterol, HDL cholesterol, triglycerides, blood pressure, waist-to-hip ratio and fasting C-peptide were not significantly different among DM, AGT and normal glucose tolerance (NGT) women. However, the C-peptide/glucose score was lower in DM than in AGT and NGT women (p < 0.01). DM or AGT women had higher prepregnancy BMI and fasting glucose level for 100g OGTT than NGT women (p < 0.05) at the time of GDM. The fasting glucose value was an independent risk factor. The cutoff point of three abnormal values in 100g OGTT provided 86% sensitivity and 43% specificity for the prediction of postpartum DM or AGT. CONCLUSIONS High prepregnancy BMI and increased glycemic deterioration at the time of GDM are found in women developing postpartum DM and AGT. The fasting glucose value for 100g OGTT is an independent risk factor and more than three abnormal glucose values offers good diagnostic efficacy in predicting postpartum glucose intolerance.