Polycystic ovary syndrome. Endoscope image of polycystic ovaries (white). The uterus is at top. Polycystic ovary syndrome (PCOS), or Stein- Leventhal syndrome, causes multiple cysts to form in the ovaries. A cyst is an abnormal fluid-filled cavity. Ovarian cysts can form when follicles fail to ovulate. PCOS develops when the ovaries are stimulated to produce excessive amounts of male hormones, particularly testosterone. Symptoms include irregular or absent menstruation, obesity and hirsutism (excessive hairiness). It is a leading cause of infertility. Treatment may be with weight loss, oral contraceptives, drugs that counter the effects of male hormones or surgery to remove hormone producing tissue.