We studied the incidence of rhegmatogenous retinal detachment in Rochester, Minnesota, for the nine-year period from 1970 through 1978. The age-adjusted rate for idiopathic rhegmatogenous retinal detachment was 10.1 per 100,000 population per year (45 cases). Including 12 cases of aphakic retinal detachments, the age-adjusted incidence was 12.9 per 100,000 population per year. Not surprisingly, the incidence rate increased with age in both sexes. By extrapolation from the Rochester rates, the number of cases per year of idiopathic retinal detachment in the United States would be expected to be about 22,000, and the number of both aphakic and idiopathic phakic cases per year would be expected to approach 28,000.