Acute encephalopathy following treatment with ifosfamide and mesna was observed in 5 (4 women and 1 men) of 28 patients (17.8%), with advanced sarcoma, lymphoma or ovarian carcinoma. This appeared within 2 to 7 days following the first dose of ifosfamide treatment, and included mental status changes, urinary incontinence, weakness, seizure activity, altered consciousness and psychiatric manifestations. Three cases were fatal, while two patients recovered completely. Brain CT and morphometric studies were normal in all the patients. Associated findings were myelosuppression, renal failure and electrolyte alterations.