In a 20-year-old patient with the classic form of Pelizaeus-Merzbacher disease, electroencephalograms during wakefulness were moderately diffusely abnormal, and an overnight polygraphic sleep recording showed distorted nonrapid eye movement sleep patterns without vertex sharp waves, K-complexes, spindles, or positive occipital sharp transients. Rapid eye movement sleep could be identified. Cerebral responses evoked by light flashes, clicks, and electric stimulation of the median nerves were abnormal.