Polycystic ovary syndrom (PCOS) is common endocrinological disorder affected large group women of reproductive age. Patogenesis of this syndrom is rather unknown. Insulin resistance accompanies very often with PCOS. Hormonal disturbances in PCOS lead to menstruation disorders, infertility and spontaneous abortion. Treatment with insulin sensitisers improves clinical pattern of women with PCOS specially treatment of infertility. Metformin reduces insulin, insulin resistance, insulin secretion, weight, testosterone and development of gestational diabetes, increases the ovulatory rate and pregnancy rate. The recent studies show beneficial effects of using metformin for women with PCOS treated during their pregnancy.