The aim of our study is to determine whether there is a relationship between familial Mediterranean fever (FMF) attacks and serum leptin levels. We enrolled 25 patients (22 males and 3 females) and 25 healthy controls (21 males and 4 females) with a mean age of 24.42 +/- 1.22 (Mean +/- SEM) years and 24.30 +/- 1.19 years (Mean +/- SEM), respectively. We investigated serum levels of leptin, interleukin-6 (IL-6), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), fibrinogen, and leukocyte counts before the attack and 8-12 hours after the attack started. The same parameters have been investigated in the control subjects. The mean serum leptin levels before the attacks were 6.45 +/- 1.05 (Mean +/- SEM) and during the attacks were 7.59 +/- 1.3 (Mean +/- SEM) in FMF group, respectively. There was a slight increase in serum leptin levels during the attacks but it was not statistically significant (P > .05). The mean serum leptin levels were 6.12 +/- 2.81 in the control group which were not different from the mean serum leptin levels before and during the attack periods in the study group (P > .05). However, there were statistical differences in the serum levels of IL-6, ESR, CRP, fibrinogen, and leukocyte counts before and during the attack periods (P < .05). No correlation was found between serum leptin levels and IL-6, ESR, CRP, fibrinogen, and leukocyte counts (P > .05). Serum leptin levels do not increase during FMF attacks and therefore it is not useful for diagnostic purposes and follow-up during treatment. Copyright (c) 2006 Bulent Toy et al.