Alterations of the ovaries easily cause diagnostic uncertainty about relevance and consequence. Palpable or sonographic ovarian tumors are reason for various differential diagnoses. Therefore the clarification of ovarian lesions is one of the main duties in daily gynaecological practice. Although diagnostic procedures might be supplemented by CT-Scan or MRI techniques, classical bimanual examination and vaginal ultrasound scan will determine the diagnosis in most cases comparably accurate. The suspected diagnosis concerning benign or malignant lesions, should take the palpable and sonographic feature, as well as the information from the patients medical history (e.g. family history of malignant diseases (BRCA 1/2 mutations) into account. In this regard, there are no other additional parameters established. Serum tumormarkers (CA 12.5) or sonographic examinations (including Doppler) have low sensitivity and specificity. Clinical diagnostic experience seems to be crucial. Cystic lesions mostly occur in premenopausal women and commonly relapse. They are mostly normal follicle cysts, but may also be a tumor of low malignant potential (LMP-tumor) or even an invasive cancerous lesion. 20-30% of all ovarian tumors are malignant and by the time of primary diagnosis already in a about 60-70% incurable due to intraabdominal dissemination. Benign or malignant lesions may occur in every age group. Ovarian tumors at infantile age are malignant in about 15%. Most malignant tumors occur between the age of 50 to 70. The LMP-tumors occur in average 10 years earlier. Malignant ovarian lesions represent about 15-30% of all genital malignant tumors. Hormonal contraceptives, pregnancy and breast feeding seem to be protective. The persistence of ovarian cysts and tumors will be mostly examined by laparoscopic surgery. In that respect the diagnosis of LMP-tumors might be incidentally and will then have a substantial impact on the extent of the surgery and the follow up. This compilation overviews the spectrum of benign and low malignant potential tumors of the ovary and their different tissues of origin.