Dimethyl sulfoxide (DMSO) has been widely used in the treatment of arthritis and certain inflammatory diseases, and is also considered an alternative remedy for cancer even if not supported by concrete evidence. This report illustrates the first case of a fatal complication following the illicit use of this agent. A 55-y-old man who reportedly ingested 500 mg acetaminophen and approximately 1 ml DMSO solution was brought to the emergency department after experiencing 2 tonic-clonic seizures. He had been diagnosed with lung mesotelioma with brain metastases which caused no neurologic deficit. The ingested DMSO was the first dose within the last 3 mo. Examination revealed right-sided hemiplegia. Unenhanced computed tomography of the head showed 3 hemorrhagic areas with blood-cerebrospinal fluid at the left parietal, occipital and frontal regions accompanied by a midline shift. Despite initial resuscitation, 2 units of fresh frozen plasma and antiedema treatment, the patient experienced cardiac arrest that did not respond to resuscitative measures. DMSO can cause massive intrametastatic hemorrhage, and neurologic deterioration can be profound in patients with metastatic brain lesions.