Mental status changes in an immunosuppressed child can be due to a variety of causes; aluminum toxicity is rarely considered. We report a teenage girl with acute lymphoblastic leukemia who developed mental status changes, speech disturbance, coarse tremor, and abnormal EEG findings following intravesical 1% alum irrigation and administration of aluminum-containing antacids. Her serum aluminum levels were mildly elevated (14-22 milligram(s), normal 0-6 milligram(s)), and bone marrow biopsy specimens demonstrated aluminum deposition on special staining (Krueger's method). All abnormalities resolved after a nine-week course of intravenous deferoxamine.