We present an in-depth study of rheumatoid arthritis (RA) in a Chippewa band. Of the 227 band members, 168 (74%) were evaluated. The unusually high prevalence of RA was confirmed in 7.1% of those studied or, minimally, 5.3% with a 100% completion rate without additional cases found. Seropositivity in those with clinically definite RA was 92% relative to rheumatoid factor and 75% for ANA. Despite the high prevalence (68%) of HLA-DR4 in this closed population, there was a significant correlation of DR4 with RA (100%). The implications of these observations in this population isolate are discussed.