['To evaluate pregnancy outcomes and its determinants in women with polycystic ovary syndrome (PCOS).', 'Two-hundred and twenty pregnant PCOS and 594 healthy women were followed from early pregnancy. Incidences of gestational diabetes mellitus (GDM), pregnancy-induced hypertension (PIH), preterm birth, twinning, and fetal growth restriction (FGR) were determined.', 'The incidence of GDM was notably higher among all PCOS combined (54.9%; OR: 2.9, 95% CI: 2.0-4.1) and PCOS subgroups, whether they conceived spontaneously (51.5%; OR: 3.3, 95% CI: 2.0-5.4), or via IVF-ET or ovarian stimulation, compared with controls (14.3%; P < 0.001). The incidence of PIH was also higher among all PCOS (10.4%; OR: 2.2, 95% CI: 1.1-4.4) and the subgroup conceiving spontaneously (11.8%; OR: 2.6, 95% CI: 1.1-6.2; P < 0.001) but not for those conceiving with IVF-ET (9.1%) or ovarian stimulation (9.4%). Lean women with PCOS (BMI <24 kg/m(2)) had higher incidences of GDM (51.1% versus 14.5%; OR: 5.6, 95% CI: 3.4-9.0) and PIH (8.9% versus 3.2%; OR: 3.0, 95% CI: 1.3-7.1) than lean controls. PCOS women with normal glucose tolerance had higher risk for PIH than their comparable control group (OR: 4.0, 95% CI: 1.3-11.7).'] Are risks for gestational diabetes mellitus and pregnancy-induced hypertension increased in polycystic ovary syndrome?