It is suggested that leptin may be involved in inflammation. Although relation between leptin levels and active pulmonary tuberculosis has been studied, there is no information about relation between leptin levels and tuberculous pleural effusions (TPE). We evaluated the diagnostic value of pleural fluid and serum leptin levels in TPE and compared them with adenosine deaminase (ADA). Forty-five patients, 17 tuberculous effusion and 28 nontuberculous effusion, with exudative pleural effusions were included. Leptin and ADA levels were measured from serum and pleural fluid in all patients. There were no statistically significant differences between tuberculous and nontuberculous groups with respect to the serum ADA activity and pleural fluid/serum leptin ratio. On the contrary, pleural fluid leptin level, pleural fluid ADA activity, serum leptin level and pleural fluid/serum ADA activity ratio were statistically different between tuberculous and nontuberculous groups. When leptin levels were corrected for body mass index, serum leptin levels did not reach statistical significance. Cut-off points to predict tuberculosis were calculated as 9.85 ng/ml and 35.55 U/l for pleural fluid leptin level and pleural fluid ADA activity, respectively. Sensitivity, specificity and area under the curve +/- standard error were 82.4%, 82.1%, 0.83 +/- 0.07 for pleural fluid leptin levels and 100%, 100%, 1.00 +/- 0.00 for pleural fluid ADA activity, respectively; the difference between these curves was significant (p = 0.01). Pleural fluid leptin levels were lower in tuberculous effusions than in other exudates. Pleural fluid leptin has a diagnostic value for TPE but not as good as that of ADA.