Two black African women and one black American man had carcinomas of cervix, perineum, and sigmoid colon, respectively. In each of these patients, trophozoites of Entamoeba histolytica had invaded the surface of the tumor, and in some areas had invaded more deeply into the stroma between the tumor cells. Although it is well known that cutaneous amebiasis of anus, penis, vulva, and cervix can mimic squamous cell carcinoma, it may be, perhaps, less well known that carcinomas at these sites may be colonized by trophozoites of E. histolytica. In patients with amebiasis but without an associated carcinoma, a correct diagnosis of amebiasis spares the patient unnecessary and sometimes mutilating surgery. But a diagnosis of amebiasis, when there is an unrecognized underlying carcinoma, delays effective treatment of the carcinoma. A smear that establishes a diagnosis of cutaneous amebiasis, therefore, should be followed by biopsy to exclude or confirm an underlying carcinoma.