A 66-year-old woman was diagnosed with a brain abscess. The abscess was drained by sterotactic catheter insertion. She was administered metronidazole at a dose of 2 g/day. On the 30th day of treatment, she had nausea that gradually progressed. On the 45th day, she developed a disturbance of consciousness and was admitted to our department. She was in stuporous state, and had slight vestibular and cerebellar dysfunctions. Diffusion-weighted and FLAIR brain MR images showed bilateral symmetrical high signals in the splenium of the corpus callosum (SCC), cerebellar dentate nucleus, and inferior colliculus. The apparent diffusion coefficient (ADC) map was reduced in the SCC, but not in the other locations. The peak of lactate on MR spectroscopy was increased in the SCC. The clinical presentation and image changes of the patient were thought to be most consistent with metronidazole toxicity. Metronidazole was discontinued, and her condition improved rapidly. She was discharged 14 days later. The lesions in her cerebellar dentate nucleus and inferior colliculus, suspected to be vasogenic edema, had disappeared 5 to 10 days later, whereas the lesion in the SCC, which gradually diminishing, could still be faintly detected 40 days later, which corresponded to our suspicion of cytotoxic edema.