Three patients complained of paroxysmal motor attacks during sleep. Videopolygraphic recordings showed that motor activity could be divided into events of increasing behavioural complexity. Simpler motor events often represented the initial fragment of more complex attacks. Clinical features suggested the attacks represented frontal lobe epileptic seizures. The attacks recurred during NREM sleep with a periodic repetition every 20-60 sec. This periodicity could be related to the analogous physiological oscillation during light sleep and the periodicity of K complexes, exerting a facilitating influence upon epileptic mechanisms.