BACKGROUND: Mapuche, Chilean natives, represent approximately 9.8% of Chilean population and in the IX region of the country, they account for 18.4% of population over 15 years old. They preserve some socio-cultural characteristics that make them different to the rest of the population. AIM: To describe the epidemiological characteristics rheumatoid arthritis among Mapuche natives. SUBJECTS AND METHODS: Retrospective review of patients of Mapuche origin with rheumatoid arthritis, seen at Temuco Hospital between 1980 and 1996. RESULTS: Among 308 cases gathered, only 106 (93 women, aged 55 +/- 10 years old) complied with 1987 American College of Rheumatology (ACR) criteria for rheumatoid arthritis. The disease began between 29 and 52 years old in 73% of patients and the mean delay in diagnosis was 4.4 years. At diagnosis, 99% had symmetric poliarthritis, 28.3% had either fatigue, fever or weight loss, and 46.9% were in class III or in class IV of ACR-1991. Fifty three percent of patients developed Sicca syndrome, 36% developed nodules, 23% developed Raynaud phenomenon, 11% developed pulmonary involvement, 7% developed vasculitis, 5% developed neurological manifestations and 19% developed ophthalmologic involvement. Rheumatoid factor was positive in 78% and 73% had erosions. HLA DR4 was (+) in 60% of 30 patients. Thirty percent required 3 or more disease modifying drugs and prednisone over 10 mg/day. There was no correlation between functional capacity and several other features of the disease. CONCLUSIONS: Mapuche rheumatoid arthritis patients are detected late and have a poor functional capacity at the time of diagnosis. They also have a higher proportion of extraarticular manifestations, more erosions and require more aggressive treatments.