• We report a case of Wiskott-Aldrich syndrome in a 31/2-year-old boy. The patient developed reticulum cell sarcoma primarily in the brain; a biopsy specimen was obtained, and treatment with irradiation and chemotherapy was begun. Computerized tomography performed after three months of therapy showed remarkable regression of tumor. When the patient died five months postoperatively, no viable tumor was present; death was the result of pneumonia and sepsis. Only two previous cases of lymphoreticular neoplasm confined to the brain and associated with this syndrome have been described. We discuss the relationship between immunodeficiency and the occurrence of neoplasia in this syndrome.