During a -4 year period, 1978-1981, 310 eyes of 301 patients living in the district of the Helsinki University Central Hospital were examined for rhegmatogenous detachment of the retina. This corresponds to an annual incidence of 6.9 per 100 000 mean population. The mean age of the patients was 54.2 years, and the sex distribution corresponded with that in the general population. The right eye was significantly (P less than 0.05) more often affected than the left eye. 78% of the eyes were phakic, and 22% were aphakic. The corresponding annual incidences were 5.4 for phakic and 1.5 for aphakic detachment per 100 000 mean population. Myopia was found in 51% of the phakic and in 24% of the aphakic eyes. The estimated annual incidence of rhegmatogenous detachment in the myopic population was more than 3 times that in the non-myopic population. The annual incidence of traumatic rhegmatogenous retinal detachment was 0.8 per 100 000 mean population. There were significant (P less than 0.005) seasonal variations in the occurrence of retinal detachment.