The overall crude incidence rate of trigeminal neuralgia per 100,000 population in Rochester, Minnesota, for 1945 through 1984 was 4.3 for both sexes combined. The age-adjusted (to total 1980 US population) rate for women (5.9) was significantly higher than that for men (3.4). Annual incidence rates increased significantly with age in both women and men. Data based on evidence in the medical records suggest that trigeminal neuralgia is a rather rare and unpredictable disease: The number of episodes varies from 1 to 11, and length of episode from 1 day to 4 years. This study indicates an elevated relative risk associated with hypertension (both overall and among women in the cohort). Also, prevalence of multiple sclerosis was significantly greater among the group of 75 patients who had trigeminal neuralgia. Since the data on treatment in this study do not correspond to a randomized clinical trial, they are presented as empirical results only and show no single treatment of choice for trigeminal neuralgia.