Continuous generalized spike-and-wave complexes occurring during slow-sleep were first observed in some children by Patry et al. (1971). A general review of the reported cases was made by Tassinari et al. (1984). We have observed a new clinical-EEGraphic picture. Spikes and spike-and-wave complexes localized to one hemisphere were recorded during at least 85% non-REM sleep both in 3 quadriplegic and in 3 hemiplegic mentally retarded children, aged from 2 years and 10 months to 11 years (mean age: 5 years and 2 months). Cyclic organization of sleep was almost normal. Wake EEG showed an epileptic focus. Brain CT showed midline defect and brain atrophy in quadriplegic patients, and a wide temporal-parietal porencephalic cyst in hemiplegic patients. This EEGraphic pattern was associated with a more pronounced mental impairment: neuropsychological improvement was observed in 2 cases, when continuous sleep discharges disappeared. As aforesaid, this picture seems to be related either to hemispheric or to midline brain defects. In our cases, sleep phase organization could be examined, while continuous generalized discharges occurring during sleep do not allow such a study.