AIMS To investigate metabolic characteristics and perinatal outcomes of gestational diabetes mellitus (GDM) in women with polycystic ovary syndrome (PCOS). METHODS We evaluated 34 GDM in women with PCOS and 70 GDM in women without PCOS in this prospective study. All GDM women were treated with medical nutrition therapy (MNT). Pre-pregnancy clinical data, fasting glucose, fasting insulin (FINS), blood lipid, homeostasis model assessment index of insulin resistance (HOMA-IR) and perinatal outcomes were investigated. RESULTS GDM in women with PCOS had higher pre-pregnancy body mass index (BMI), higher incidence of overweight than in the non-PCOS group (each P<0.001). Incidence of history of infertility was also significantly higher in the PCOS group than in the non-PCOS group (20.6% vs. 2.9%, P<0.01). A higher incidence of early pregnancy loss (EPL) was found in the PCOS group than in the non-PCOS group (20.6% vs. 7.1%, P<0.05). Significantly higher in vitro fertilization and embryo transfer (IVF-ET) rate and insulin administration was also observed in the PCOS group than in the controls. No significant difference was found in the prevalence of preeclampsia, premature delivery, macrosomia, fetal death and neonatal congenital anomaly between GDM in women with and without PCOS (all P>0.05). [corrected] CONCLUSIONS Compared with the controls, no significant increase in the incidence of adverse perinatal outcomes was detected in GDM in women with PCOS by appropriate management.