To obtain information on changes in the age distribution of new cases of rheumatoid arthritis (RA) in Finland.
The present study covered those subjects entitled under the nationwide sickness insurance scheme to receive specially reimbursed medication for RA in 5/21 central hospital districts in Finland (population base about one million adults) in 1975, 1980, 1985, and 1990.
During the four study years 1321 incident cases occurred, which satisfied the American Rheumatism Association 1987 classification criteria for RA. The mean age at diagnosis increased by 7.6 years from 1975 (50.2 years) to 1990 (57.8 years). No appreciable differences occurred between men and women. The incidence rates declined in the younger age groups.
The epidemiology of RA is in a dynamic state. The trends may reflect marked changes in the host-environment relationship.