Rheumatoid arthritis (RA) is a chronic inflammatory disease in which interleukin (IL)-10 plays an important role. There are, however, controversial reports that IL-10 promoter polymorphism may be an independent marker of susceptibility and severity of RA. The aim of the present study was to examine the IL-10 promoter polymorphism in patients with RA. We examined 95 patients with rheumatoid arthritis diagnosed according to the criteria of the American College of Rheumatology. Polymerase chain reaction amplification was used for analysis of the promoter polymorphism of the IL-10 gene. In RA patients, the prevalence of genotypes encoding high expression of IL-10 was observed. Nevertheless, there was no association between IL-10 genotypes and age at disease diagnosis, disease activity in a physician's global assessment, and joint and extra-articular involvement. There was also no correlation between IL-10 polymorphism and disease activity parameters--erythrocyte sedimentation rate, C-reactive protein, number of swollen and tender joints, and duration of morning stiffness. We suggest that IL-10 promoter polymorphism is not a genetic risk factor for RA activity.