Four cases of endosalpingiosis presenting as masses that resembled neoplasms are described in women 20, 41, 43, and 74 years of age. Each case was referred in consultation because of difficulties in pathologic diagnosis. In two patients, multiple cysts that involved the serosal surfaces of the uterus and adnexa in one case, and the colon, rectosigmoid, pelvic sidewalls, and the cul-de-sac in the other, were excised. In the other two cases, hysterectomy was performed for an enlarged cystic cervix in one case and presumed uterine leiomyomas in the other. In both of these cases, the uterine cervix and lower part of the uterine corpus were extensively involved by multiple cysts on gross examination, and in one of them, a frozen section of the cervical lesion was initially interpreted as "suspicious for invasive minimal deviation adenocarcinoma." On microscopic examination, benign endosalpingiotic glands and cysts were found in all four cases, with striking transmural involvement of the uterine cervix and lower uterine segment and contiguous corpus in the two cases with uterine involvement. The latter two cases are the first examples, to our knowledge, of endosalpingiosis involving the wall of the uterus; the differential diagnosis in these cases includes minimal deviation adenocarcinoma and florid tubal metaplasia with cystification. The four cases in this report, and rare previously reported cases, indicate that although usually a microscopic finding, endosalpingiosis can rarely present as a clinically or grossly evident mass that can be confused with a neoplasm.