The purpose of this work was to compare pre- and post-operative facial nerve function between unmonitored and monitored cases of skull base lesions. The study involved 32 patients suffering from lateral skull base tumours (10 unmonitored and 22 monitored). Facial nerve function was monitored intraoperatively by an acoustic facial electromyographic system (NIM-2). Post-operative facial function was graded according to the House-Brackmann scale. In the group of monitored cases, facial nerve function was normal (Grade 1 or 2) in 79 per cent of the patients, while the unmonitored patients showed normal function in only 50 per cent of the cases. These results confirm previous observations that audible evoked electromyographic monitoring significantly reduces permanent facial nerve dysfunction.