Abstract Aim: To evaluate endometrial histologic morphology in patients with polycystic ovary syndrome. Material and methods: 93 women, aged 18-35, who were hospitalized in the Gynaecologic Endocrinology Department of Warsaw Medical University due to PCOS have been qualified for the research. All patients had menstrual pattern of oligomenorrhoea and mean cycle length of 49+/-38 days. The control group consisted of 40 healthy women with regular menstrual cycles and no symptoms of hyperandrogenism. In case of each patient the fallowing data were analyzed: age, menarche age, Body Mass Index and endometrium histologic findings. The endometrium was aspirated using the Pipelle probe. Statistic analysis was performed and the values of p<0,05 were deemed statistically significant. Results: No statistical significance was found between the age of the patients, their menarche age and BMI. Proliferative endometrium was significantly more often observed (p<0.01) in patients with PCOS (64.52 %) than in the control group (15%). Secretory endometrium was found in 23.65 % of the examined patients. This result differed statistically from the 85 % rate in the control group (p<0.01). In case of PCOS patients, mixed type endometrium was found in 10 patients (10.75%) and simple endometrial hyperplasia without atypia was found in 1 patient (1.08%). Conclusions: 1. Lack of ovulation or late ovulation play a crucial role in endometrial cyclic transformation and its disorders. 2. The prolonged endometrial proliferation phase is a characteristic feature of women suffering from PCOS.