The incidence of acute closed-angle glaucoma was studied in 1796 patients derived from the hospital discharge registry of Finland for the years 1973-1982 (469 males and 1327 females). The average incidence was 3.8 cases/100,000 per year. The incidence showed a steep rise with age. The highest incidence was observed in both sexes in the group 80 years of age and older. The incidence was higher (Chi-square 7.81, df = 1, P less than 0.01) among women (5.3/100,000 per year) than among men (2.0/100,000 per year). The age-adjusted incidence for the whole period of 1973-1982 showed no statistically significant rise. The seasonal variation of incidence was statistically significant (P less than 0.001). In winter (December, January, February) and in autumn (September, October, November) the incidences were higher compared to spring (March, April, May) and summer (June, July, August). This association was greater (P less than 0.001) among females than among males (P less than 0.05). Mean sunshine hours showed a reverse association with the incidence of acute glaucoma. The association was statistically significant when both sexes were pooled together (P less than 0.001). There was no sex interaction with regard to the association of incidence of acute glaucoma and mean sunshine hours.