['To test the hypothesis that the risk of persistent glucose impairment after gestational diabetes mellitus (GDM) is increased in patients with polycystic ovary syndrome (PCOS).', 'The prospective case-control study included 42 pregnant patients with PCOS and GDM and 84 pregnant control patients with GDM but without clinical and biochemical hyperandrogenism, polycystic ovaries, and oligo-anovulation. The case and control subjects were matched one to two for age and BMI. The glycemic profiles were studied in all subjects 6 weeks, 12 weeks, and 18 months after delivery. The incidence and the relative risk (RR) were calculated for overall persistence of an abnormal glycemic pattern and for each specific alteration, i.e., impaired glucose tolerance (IGT), impaired fasting glucose (IFG), and diabetes mellitus (DM).', 'At 18 months after delivery, the incidences of IFG, IGT, and IFG-IGT were significantly (P < 0.05) higher in the cases than in the controls. At the 18-month follow-up, the RR for the composite outcome of glucose metabolism impairment in PCOS women was 3.45 (95% CI 1.82-6.58).'] Is the risk of a persistent glucose metabolism impairment after gestational diabetes mellitus increased in patients with polycystic ovary syndrome?