The aim of this study was to examine the association between plasma retinol-binding protein 4 (RBP4) and gestational diabetes mellitus (GDM) and the risk of developing metabolic syndrome after pregnancy. In a case-control study, 192 pregnant women (92 with GDM) were recruited. Gestational diabetes mellitus was diagnosed based on O'Sullivan and Mahan criteria. In all pregnancies, plasma RBP4 concentrations were measured. Retinol-binding protein 4 concentrations in GDM patients were significantly higher than the normal women. Retinol-binding protein 4 level equal to or more than 42 microg/mL could help predict the risk of developing GDM (sensitivity = 75.8%, specificity = 65.3%, P = .001). Concerning metabolic syndrome after pregnancy, in all participants, the prevalence of metabolic syndrome base on World Health Organization (WHO) criteria was 24%. After pregnancy, 32.6% of women with GDM had metabolic syndrome compared with 10.5% of those with healthy pregnancy (P = .001). Age more than 25 years, body mass index (BMI) more than 27 kg/cm(2), and RBP4 concentrations were independent risk factors for GDM. Measurement of RBP4 together with the assessment of other risk factors could help identify women at risk of developing GDM.