Fourteen patients with hemifacial spasm were submitted to surgical exposure and neurolysis of the seventh nerve at the cerebellopontine angle. Seven patients had an anomalous anterior inferior cerebellar artery pulsating on the nerve, being present in one patient also Arnold-Chiari malformation. Another patient had chronic arachnoiditis involving the facial nerve. In 6 patients no abnormalities were found in the posterior fossa. There was complete relief of the spasm in 10 patients, 2 were unchanged, 1 had recurrence 10 months later and 1 died in the post-operative period due to head injury sustained during a fall.