Infective endocarditis is a serious bacterial infection, but there are relatively few data about its occurrence and prognosis. The incidence rate, 30-d case fatality and mortality rate of infective endocarditis were estimated in this registry-based cohort study. The Danish National Registry of Patients was used to estimate national incidence rates, and information on the date of death was obtained through linkage to the Civil Registration System. The study included 3351 patients with infective endocarditis from 1980 to 1997. The incidence rate for men increased from 4 to 6 per 100,000 person-years, and for women from 3 to 4 per 100,000 person-years. The mean incidence rate varied from 1.5 per 100,000 person-years in women younger than 50 y to 15.5 in men older than 70 y. The incidence increased in most age groups but was most pronounced in younger men. The overall 30-d case fatality rate of 23% increased with age and decreased with calendar time. The mean mortality rate was 0.94 per 100,000 y and decreased in the study period in most age groups. There was an increasing incidence of infective endocarditis and an improvement in the prognosis.