Objective The purpose of this study was to identify a clinical parameters were predictive for a high risk of diabetes mellitus in women with recent gestational diabetes mellitus. Methods One hundred women underwent an oral glucose tolerance test within 28~32 weeks of the pregnancy. Demographic, historic, and antenatal glycemic parameters were tested. Results Gestational diabetes mellitus was diagnosed in 23 women (23%) according to the American Diabetes Association criteria (1997). No maternal demographic or neonatal parameters were significantly associated with diabetes mellitus. The final model of independent predictors in decreasing significance included the highest fasting plasma glucose level during pregnancy, any fasting plasma glucose level of > or = 105 mg/dL (class A(2)), the area under the curve of pregnancy oral glucose tolerance test, gestational age at diagnosis, previous gestational diabetes mellitus history, and 50-g glucose challenge test results. The fasting plasma glucose level was the best discriminator, with a 21-fold (95% CI, 4.6~96.3) increased odds ratio comparing the 4th quartile (fasting plasma glucose level, > 121 mg/dL; diabetes mellitus rate, 36.7%) to 1st quartile (fasting plasma glucose level, < 95 mg/dL; diabetes mellitus rate, 0.5%). Conclusion During pregnancy, the highest fasting glucose level, followed by the severity of glucose intolerance were the best predictors for gestational diabetes mellitus. Diabetic education should begin during pregnancy, especially for women who are identified to be at a high risk when they are highly motivated and under medical care.