We compared the prevalence of diabetes in women who experienced gestational diabetes mellitus (GDM) with that in the general population and identified risk factors for the development of diabetes. The analysis included 868 subjects (620 GDM and 248 single positive (SP) for one of the diagnostic criteria). The post-partum examinations included 2 h 75 g oral glucose tolerance tests, lipid profiles, anthropometric measurements, and documentation of medical history, diet, and lifestyle. All participants were followed up at 6 weeks after parturition and subsequent follow-ups were conducted annually. General population subjects were identified from the 2001 Korean National Health and Nutrition Survey and age-matched for case-control analysis. Eleven (4.4%) and 71 (11.5%) subjects in the SP and GDM groups, respectively, developed diabetes, while 22 (2.5%) subjects in the general population group presented with diabetes. The risk of developing diabetes was 3.5 times greater for GDM subjects than for general population subjects, after adjusting for confounding factors. A multiple logistic regression model revealed that GDM, a family history of diabetes, and waist circumference were independently associated with the development of diabetes. We concluded that GDM women in Korea are at high risk of diabetes irrespective of the absence of putative risk factors.