Leptin is an adypocyte derivated peptide hormone that plays a major role in preventing obesity development by the effects at the hypothalamic level. In our study leptin levels of 41 rheumatoid arthritis (RA) patients and 25 healthy subjects as control group were assessed. Synovial fluid from 21 RA patients were collected to detect leptin levels. Synovial fluid and plasma leptin levels were analysed and correlated with RA duration, ESR, CRP, X ray changes (erosive or non-erosive disease) and negative or positive test for rheumatoid factor. There wasn't any significant difference at plasma leptin levels between RA patients (3.91 +/- 6.15) and control group (4.94 +/- 6.44) (p > 0.05). Plasma leptin levels were correlated with body mass index (BMI) in both healthy subjects and RA patients (r = 0.37; p = 0.018). Therefore in RA patients, plasma and synovial fluid leptin levels were not correlated with disease duration, ESR, CRP, negative or positive test for rheumatoid factor and erosive or non-erosive disease (p > 0.05). In conclusion leptin is correlated with BMI both in RA patients and healthy individuals but no considerable relation with disease activity.