Two patients with uncontrollable aggressive behaviour underwent the placement of stimulating leads in the posterior hypothalamus (pHyp). One patient had also multifocal refractory epilepsy. Microrecordings were obtained in both patients during surgery under general anaesthesia. Firing rate, interspike intervals and oscillatory discharge patterns were analysed in 14 neurons. A mean discharge rate of 19 Hz, and oscillatory activity at 7-8 Hz were recorded in the first patient with aggressiveness and epilepsy. In the second patient the mean firing rate was 10 Hz, with evidence of both tonic and random firing patterns. Previous studies in patients with cluster headache showed that a discharge rate around 20 Hz and lack of a specific rhythmic pattern were the most consistent characteristics of neuronal discharge in this area. Our present findings therefore would suggest that the pattern of discharge of neurons in the pHyp should be evaluated with reference to the presence of concurrent pathology.