Adnexal masses are frequently found in both symptomatic and asymptomatic women. In premenopausal women, physiologic follicular cysts and corpus luteum cysts are the most common adnexal masses, but the possibility of ectopic pregnancy must always be considered. Other masses in this age group include endometriomas, polycystic ovaries, tubo-ovarian lan abscesses and benign neoplasms. Malignant neoplasms are uncommon in younger women but become more frequent with increasing age. In postmenopausal women with adnexal masses, both primary and secondary neoplasms must be considered, along with leiomyomas, ovarian fibromas and other lesions such as diverticular abscesses. Information from the history, physical examination, ultrasound evaluation and selected laboratory tests will enable the physician to find the most likely cause of an adnexal mass. Measurement of serum CA-125 is a useful test for ovarian malignancy in postmenopausal women with pelvic masses. Asymptomatic premenopausal patients with simple ovarian cysts less than IO cm in diameter can be observed or placed on suppressive therapy with oral contraceptives. Postmenopausal women with simple cysts less than 3 cm in diameter may also be followed, provided the serum CA-125 level is not elevated and the patient has no signs or symptoms suggestive malignancy.