Obesity is a modifiable major cause of morbidity and mortality in the general population, but little is known about the association of obesity and quality of life in patients with rheumatoid arthritis (RA). Thus, we set out a study to test the hypothesis that obesity is independently associated with lower quality of life in patients with RA. Three hundred and fifty nine patients with RA underwent an interview, physical exam, and all clinical charts were reviewed. Based on body mass index (BMI), patients were classified as normal (BMI < 25 kg/m(2)), overweight (BMI = 25-29.9 kg/m(2)), and obese (BMI > or = 30 kg/m(2)). Quality of life was quantified with the Medical Outcomes Study Short Form 36 (SF-36). Data obtained included demographic variables, extra-articular disease, comorbidities, presence of X-ray erosions, rheumatoid factor, and depression. The association between obesity and quality of life was examined with the use of multiple lineal regression models. One hundred and seventy-two patients (47.9%) had normal BMI, 126 (35.1%) were overweight, and 61 patients (17%) were obese. Obese patients had lower quality of life (30.8 +/- 18.1) than overweight patients (43.3 +/- 20.1) and patients with normal weight (43.8 +/- 22.2), P < 0.001. The association between obesity and impaired quality of life was confirmed with a linear regression model (Coef = -12.9, P < 0.001) and remained significant after adjustment for age, sex, disease activity, extra-articular disease, comorbidities, X-ray erosions, presence of rheumatoid factor, depression, education, and disease duration (Coef = -5.3, P = 0.039). In conclusion, obesity is independently associated with the impaired quality of life in patients with rheumatoid arthritis.