Leptin which is the product of Ob gene derived from adipocytes is a hormone with roles in energy balance, appetite and it has close ties with endocrine as well as metabolic systems. Relationship between leptin and prostate cancer and benign Prostatic hyperplasia (BPH) is currently under investigation. In the present study we investigated whether leptin can be used as a tumor marker for diagnosis and prognosis of prostatic diseases. 23 healthy young volunteers (Group A), 43 healthy aged volunteers (Grup B), 23 patients with PCa (Group C), 23 patients with BPH were recruited into the study. Serum leptin, f-PSA, t-PSA, total cholesterol (Chol), triglyceride , HDL-chol, VLDL-chol, VLDL-chol levels were determined in all groups. When serum leptin and leptin/BMI were analyzed, there was a statistically significant increase in Group B compared to Group C (p<0.05). Correlation among leptin and leptin/BMI and other biochemical parameters were analyzed in each group separately. In Group A, there was a positive correlation between leptin and f-PSA, and t-PSA (r:0.460, p=0.027, r:0.583, p=0.003; respectively). In Group B, there was a positive correlation between leptin and triglyceride, and VLDL-chol (r:0.471, p=0.031, r:0.475, p=0.029; respectively). When correlation between leptin/BMI and f-PSA, and t-PSA levels were analyzed, there was a positive corelation between leptin/BMI and f-PSA in group A (r:0604, p=0.002). In conclusion, although the relationship between leptin and prostate physiology and pathology is not clearly deciphered yet based on todays limited literature, more comprehensive advanced studies with large number of patients are needed to further examine this issue. ©2004, Fırat Üniversitesi, Tıp Fakültesi