A series of 152 posterior fossa explorations for tic douloureux and hemifacial spasm has been reviewed with assessment of outcome at the last follow-up examination. Among 103 cases of tic followed for an average of 48.3 months, 79 patients (77%) obtained good or excellent symptomatic relief, and there were 24 failures or recurrences (23%). Of 48 cases of hemifacial spasm followed for an average of 42.1 months, there were good or excellent results in 42 cases (87.5%); only 6 patients (12.5%) experienced failure or recurrence. Patients noted to have arterial contact at the 5th nerve entry zone responded significantly better to microvascular decompression than did patients with no arterial contact. Further, patients noted to have anatomical distortion of the 5th nerve by an artery or wedging of an artery into the crevice between the nerve and the pons had significantly better outcomes after microvascular decompression than did patients with other kinds of arterial contact. Partial sensory rhizotomy proved to be a highly effective alternative to microvascular decompression in cases of doubtful neurovascular compression. It was not possible to define similar neuroanatomical criteria predictive of response to microvascular decompression in patients with hemifacial spasm.