Forty leukemic patients with inflammatory anorectal complications were examined. Twenty two were affected by acute lymphatic leukemia, 10 by chronic lymphatic leukemia, 6 by acute myelocytic leukemia and 2 by non H lymphoma and chronic myelocytic leukemia, respectively. In all cases surgery was indicated not only to treat the anorectal complication, but mainly to resume the antiblastic chemotherapy discontinued because of the risk of sepsis and to prevent the failure of bone marrow transplantation in patients with chronic myelocytic leukemia. The underlying malignant disease and the altered platelet, white blood cell and neutrophil levels were shown to be the major factors conditioning the surgical treatment. In 2 cases, acute recurrence of the underlying disease and the development of a graft verus host disease have been the cause of death. It is concluded that in patients eligible for bone marrow transplantation or undergoing radio and/or chemotherapy, local and general antinfective prophylaxis is of paramount importance to decrease the risk of inflammatory anorectal complications.