In 200 patients, 143 women and 57 men, with rheumatoid arthritis (RA), age at onset was related to the presence of IgM rheumatoid factor (RF) and antinuclear antibodies (ANA) in serum at presentation. The patients were stratified into bands of age at onset: <40 years, 40- 60 years, and >60 years. In women, the prevalences of ANA (1:160) were 63.0%, 45.5%, and 31.1% in the respective age bands ( p=0.002), and the prevalences of IgM RF were 85.2%, 72.7% and 66.4%, respectively ( p=0.03). The prevalences of ANA and IgM RF among men were, respectively, 35% and 86% with no association with age at onset. The findings may indicate interactive effects between gender and various pathogenetic factors.