We tested the traditional format of the American Rheumatism Association (ARA) 1987 revised criteria for the classification of rheumatoid arthritis (RA) in a cohort of 220 subjects with drug reimbursement for chronic rheumatic diseases extracted from the National Sickness Insurance Register, in a community of 18,000 people in Finland. One hundred and nine of the 193 who consented to the study both met the new ARA criteria for RA and had disease onset after 16 years of age, giving a cumulative prevalence of 0.8% in the population of 13,300 over 16 years. The disease of 6 of them, however, fulfilled the criteria and clinical picture of some other rheumatic disease. Thus 103 patients had RA as the only diagnosis. The female:male ratio in the 103 patients was 1.7:1. Ninety-one (88%) had seropositivity at some time in their disease and 99 (96%) had erosive joint disease. In most instances the 12 seronegatives had either mild or nontypical RA and only one of them was male. The 103 patients who met the new ARA criteria had significantly more interventions, such as hospitalization, drug treatment and orthopedic surgery, than the subjects (n = 42) who despite a clinician's primary diagnosis of RA did not fulfill the criteria. Thus the new ARA criteria distinguish clinical and severe cases of RA from nonclinical or non-RA cases when applied to a population based cohort of subjects with chronic rheumatic diseases registered for drug reimbursement.