To assess the value of magnetic resonance imaging in the evaluation of trigeminal neuralgia, 51 patients were studied by magnetic resonance imaging after a trigeminal protocol. Clinical and magnetic resonance imaging results were correlated. Seventeen (33%) nonvascular abnormalities and 27 (53%) vascular contacts or compressions of the trigeminal nerve were demonstrated. Of the patients younger than of 29 and 39 years of age, 100% and 45%, respectively, had a tumor or multiple sclerosis compared with 20% and 18% of those older than 40 and 60 years of age, respectively. One third of the patients with pain in more than one branch of the trigeminal nerve had tumors. On the basis of this study, magnetic resonance imaging may be useful in discovering underlying pathoses associated with trigeminal neuralgia if patients have failed to respond to an initial conservative treatment. The patients most likely to exhibit significant magnetic imaging resonance findings are young and with pain in more than one trigeminal branch.