Clinical hepatitis B among hospital staff in Sweden was studied in a 15-year follow-up, divided into three periods. During the first 5-year period, 1969-1973, 756 cases of hepatitis B were reported among hospital staff, for an attack rate of 102.0 per 100,000 person-years. In the second five-year period, 1974-1978, the attack rate was 30.4, and in the last five-year period, 1979-1983, it was 10.4. The decrease in incidence between the first period and the second was significant (p less than 0.001), as was the difference between the second period and the last (p less than 0.01). The difference between the incidence in medical personnel and that in the general population of working age in the first period was significant at p less than 0.001 and during the last period it was significant at p less than 0.01. No statistical significance was found during the second period, due to the decrease in incidence for both groups, which made the values too scattered. Traditionally high-risk units, such as renal dialysis units, had only three cases reported in the last 5-year period. An overrepresentation of males among nurses and nursing assistants with acute hepatitis B was found.