A 4-year study (January 1986 through December 1990) was performed to evaluate the cytomorphologic features of cystic ovarian lesions. Fluid from 103 cases was obtained either during surgical removal of the ovary (48 cases; mean age 50 years) or by fine needle aspiration (55 cases; mean age 32 years). Of the 48 cystic lesions with histologic correlation, 30 (62.5%) were neoplastic and 18 (37.5%) were non-neoplastic. Ten (18%) of the 55 aspirates were unsatisfactory. The remaining 45 cases (82%) were benign, predominantly non-neoplastic entities which included follicle, corpora luteal, and endometriotic cysts. Neoplastic cystic lesions included serous, mucinous, and Brenner tumors, germ cell neoplasms, a sex cord-stromal tumor, and an undifferentiated carcinoma. Follicle and corpora luteal cysts were composed of loose cell clusters of granulosa cells and/or luteinized granulosa cells. Endometriotic cysts contained hemosiderin-laden macrophages and endometrial cells. Serous and mucinous cystadenomas were composed of cohesive sheets and/or papillary clusters of epithelial cells. A cystic Brenner tumor showed sheets of cells with grooved nuclei, and a benign cystic teratoma contained mature squamous cells admixed with vacuolated cells of presumed sebaceous origin. Although the distinction between benign and malignant entities posed few diagnostic difficulties, borderline tumors could not be distinguished from well-differentiated cystadenocarcinomas. The results of this study indicate that the majority of cystic ovarian lesions can be diagnosed accurately on cytology. Cytologic evaluation of non-neoplastic ovarian cysts is important for women who want to retain their fertility and in the clinical management of women with neoplastic lesions.(ABSTRACT TRUNCATED AT 250 WORDS)