Sleep and sleep spindle parameters were examined in 15 children with primary generalized spike-and-wave discharges at University Hospitals, Leuven, Belgium. Nine were untreated and 6 were treated. Compared to a nonepileptic control group, untreated epileptic patients had a significantly shorter stage 2 onset and less sleep spindles in stage 2. Less fast frequency spindles were observed in the last stage 2 period of the night. In the treated group of patients, sleep patterns were comparable to controls. Sleep architecture dysfunctions, common in generalized epilepsy, may be predicted by the sleep spindle abnormalities observed in the EEG. [1]