We report here on the clinical courses of three cases of acute appendicitis during a period of myelosuppression after chemotherapy for acute leukemia. The patients were two boys and one girl with a mean age 11 years (range, 10-12). Two of the patients had acute myeloid leukemia (AML) in subtypes M1 and M2, while the third had acute lymphoblostic leukemia of subtype L1 (FAB classification). All patients had clinical features of fever, abdominal pain, and elevations of C-reactive protein. However, the typical peritoneal signs were blunted and developed transiently in two cases. All patients were diagnosed as having appendicitis with abdominal computed tomography scan (CT), and proceeded to appendectomy. With perioperative support utilizing antibiotics, antifungal agents, blood components, and granulocyte-colony stimulating factor, surgical intervention was successfully performed, and all patients were able to undergo chemotherapy courses shortly after surgery. Histological examinations of the appendectomy specimens showed infiltration of most of the lymphoid cells and a few neutrophils in the wall of the appendix. Enhanced CT was useful in diagnosing appendicitis, which needs to be considered in cases presenting with clinical symptoms such as described here. Because of a high mortality rate after appendix perforation, immediate surgical intervention with sufficient perioperative support should be performed.