A 16-year-old male started on isotretinoin 80 mg daily for acne developed persistent headache 3 weeks later, with myoclonus and confusion 10 weeks later. During initial hospital assessment his Glasgow Coma Scale score fell acutely to 8 and he required ventilation. Brain imaging and cerebrospinal fluid (CSF) analysis were normal and an electroencephalogram (EEG) showed features of encephalopathy. No cause was found. He was extubated after 24 hours and made a full recovery. This is the first report of a generalized encephalopathy thought likely to be due to isotretinoin.