Outcome after 252 posterior fossa explorations for the treatment of trigeminal neuralgia was determined by a retrospective review. Patients with distortion of the fifth nerve root caused by extrinsic vascular compression underwent microvascular decompression, those with no compression underwent partial sensory rhizotomy, and those with vascular contact but no distortion of the nerve root underwent decompression and rhizotomy. The mean follow-up period was 5.1 years. An excellent (75%) or good (8%) clinical outcome was achieved in 208 patients; 13 patients (5%) experienced little or no pain relief. Thirty-one patients (12%) suffered recurrent trigeminal neuralgia an average of 1.9 pain-free years after operation; recurrence continued at a rate of approximately 2% per year thereafter. Reoperation for recurrent or persistent pain provided excellent or good results in 85% of reoperated patients, but partial sensory rhizotomy was required in most of these patients. Outcome was affected by previous surgical procedures. A previous percutaneous radiofrequency lesion was associated with a significantly greater incidence of fifth nerve complications and a worse outcome after posterior fossa exploration. Because of this finding, the authors recommend that percutaneous radiofrequency rhizolysis be reserved for patients who have failed posterior fossa exploration or who are not candidates for surgery. Patients with compressive nerve root distortion and a short duration of symptoms before surgery had a significantly better outcome than patients with a longer duration of symptoms. In contrast, there was no relationship between the duration of symptoms and outcome of patients without nerve root distortion. Vascular decompression may cause dysfunction of the trigeminal system in tic douloureux, but in patients who remain untreated for long periods an intrinsic abnormality develops that may perpetuate pain even after microvascular decompression. Posterior fossa exploration is recommended as the procedure of choice for patients with trigeminal neuralgia who are surgical candidates.