OBJECTIVES: This study was performed to evaluate serum leptin levels in rheumatoid arthritis (RA) patients and investigate the correlation with serum tumor necrosis factor alpha (TNF-alpha) levels and clinical and laboratory parameters of disease activity. METHODS: Fifty patients with RA and 34 control subjects were included. Disease activity score 28 (DAS28) was calculated for each patient. Laboratory activity was assessed by examining erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). Immunoradiometric assay was used for measuring serum leptin levels (ng/mL). Serum TNF-alpha levels (pg/mL) were measured by sandwich enzyme-linked immunosorbent assay method in 41 of 50 RA patients and in 24 control subjects. RESULTS: Age, sex and body mass index (BMI) did not show a statistically significant difference between RA and control subjects (P > 0.05). Serum leptin levels were higher in RA (P = 0.000). In RA patients, there were no correlations between serum leptin levels and disease duration, swollen and tender joint counts, DAS28, CRP, ESR, serum TNF-alpha levels, oral glucocorticoid and methotrexate usage (P > 0.05). There was no statistically significant serum leptin level difference between patients with high disease activity and mild and low disease activity (P = 0.892). Serum leptin levels positively correlated with BMI in both patient and control groups (P < 0.05). In both groups, mean serum leptin levels were higher in women than men. CONCLUSIONS: Even though serum leptin levels were found to be significantly higher in RA patients than in control subjects in this study, there was no correlation between serum leptin levels and TNF-alpha levels, clinical and laboratory parameters of disease activity. However serum leptin levels positively correlated with BMI in both patient and control groups. In RA, circulating leptin levels do not seem to reflect disease activity.