Four cases of benign cystic mesothelioma are described. The disease affects young white women (mean age, 30 years), and they present with chronic pelvic pain. At laparoscopy or laparotomy, multiple cysts ranging in size from 0.5 to 4 cm in diameter and containing clear fluid are seen. The disease commonly affects the pelvic organs and/or omentum. With the electron microscope, the cell of origin of this proliferative process is shown to be the mesothelial cell. The disease has been previously described under a variety of terms. There seems to be a tendency for recurrence, but no malignant potential is apparent. Treatment may be conservative with preservation of pelvic organs. Benign cystic mesothelioma should be considered in the differential diagnosis of cystic lesions of the female genital tract.