A case is presented of Kleine-Levin syndrome observed over 5 years in which a large number of EEG records were made both during and between attacks. In contrast with most reported cases the serial records made during an attack revealed an abnormality. This consisted in bursts of slow waves, more prominent in the posterior region, with a quantitative decrease of the abnormality towards the end of the attack. Waking records between attacks were entirely normal. A sleep record made between attacks revealed distinct spike discharges, more prominent on the left. The possibility that there is a relationship between the Kleine-Levin syndrome and the convulsive disorders is considered and discussed. © 1969.