Endometriosis is a common disease in middle-aged women. The main cause of ailments are endometrial cells present outside the uterine cavity. Most commonly these cells can be found in pelvis but occasionally in more distant areas of body. Physiological fluctuations of sex hormones lead to periodical changes in ectopic cells: proliferation, bleeding, inflammation and finally cicatrization. All these changes evoke characteristic symptoms: pain in lower parts of abdomen, painful menstruation and infertility. Although we know all these symptoms, very occasionally history data and gynecological examination are sufficient to make the right diagnosis. The main aim of this investigation is to estimate the usefulness of transvaginal ultrasound imaging in diagnosis of ovarian endometriotic cysts.