Reports regarding the association between body composition and inflammatory activity in rheumatoid arthritis (RA) have consistently yielded contradictory results. To perform a systematic review on the association between overweight/obesity and inflammatory activity in RA. FAST approach: Article search (Medline, EBSCO, Cochrane Library), followed by abstract retrieval, full text review and blinded assessment of methodological quality for final inclusion. Because of marked heterogeneity in statistical approach and RA activity assessment method, a meta-analysis could not be done. Results are presented as qualitative synthesis. One hundred and nineteen reports were found, 16 of them qualified for full text review. Eleven studies (8,147 patients; n range: 37-5,161) approved the methodological quality filter and were finally included. Interobserver agreement for methodological quality score (ICC: 0.93; 95% CI: 0.82-0.98; P.001) was excellent. In all reports body composition was assessed by BMI; however a marked heterogeneity was found in the method used for RA activity assessment. A significant association between BMI and RA activity was found in 6 reports having larger mean sample size: 1,274 (range: 140-5,161). On the other hand, this association was not found in 5 studies having lower mean sample size: 100 (range: 7-150). The modulation of RA clinical status by body fat mass is suggested because a significant association was found between BMI and inflammatory activity in those reports with a trend toward higher statistical power. The relationship between body composition and clinical activity in RA requires be approached with further studies with higher methodological quality. Copyright © 2015 Elsevier España, S.L.U. and Sociedad Española de Reumatología y Colegio Mexicano de Reumatología. All rights reserved.