OBJECTIVE: To investigate adverse pregnancy outcomes in non-obese women with polycystic ovary syndrome (PCOS) compared with obese-PCOS and control groups. METHODS: Women with PCOS who underwent assisted reproductive technology (ART) from August, 2003 to December, 2007, were considered. A total of 336 women with PCOS were included in the study group and 1,003 infertile women who had tubal factor as an indication for ART were collected as controls. They were divided into four groups: a non-obese PCOS group, obese-PCOS group, non-obese tubal factor group, and obese tubal factor group, with obesity defined by a body mass index over 25 kg/m2, and reviewed focusing on the basal characteristics, ART outcomes, and adverse pregnancy outcomes. RESULTS: There was no difference among the groups' the clinical pregnancy rate or live birth rate. Regarding adverse pregnancy outcomes, the miscarriage rate, multiple pregnancy rate, and prevalence of preterm delivery and pregnancy induced hypertension were not different among the four groups. The incidence of small for gestational age infant was higher in the PCOS groups than the tubal factor groups (p<0.02). On the other hand, the morbidity of gestational diabetes mellitus (GDM) was not high in the non-obese PCOS group but was in the obese groups. And in the obese PCOS group, the newborns were heavier than in the other groups (p<0.02). CONCLUSION: Non-obese PCOS presents many differences compared with obese PCOS, not only in the IVF-parameters but also in the morbidity of adverse pregnancy outcomes, especially in GDM and fetal macrosomia.