Purpose: Expression of recently identified growth hormone-releasing peptide, ghrelin, and its receptor has been demonstrated in prostate cancer (PCA) cell lines. It was also shown that ghrelin has increased cell proliferation in vitro when added to PCA cell lines. The aim of this study was to evaluate the diagnostic value of serum ghrelin levels in detection of PCA. Material and Method: 30 patients with PCA and 50 patients with benign prostate hyperplasia (BPH) were enrolled in the study. The serum ghrelin levels of PCA and BPH patients were compared. The correlations between ghrelin and age groups, body mass index, total prostate-specific antigen (PSA) levels, free/total PSA ratio, Gleason score, and prostate volume were also studied. Results: There were no statistically significant differences between the two groups and parameters mentioned above in terms of serum ghrelin levels (p > 0.05). Conclusion: Although ghrelin has been shown to induce PCA cell proliferation by in vitro studies, its role in the diagnosis of PCA was not demonstrated in our clinical study. Insufficient secretion of ghrelin into serum or the effect of other sources of ghrelin to serum ghrelin levels could be responsible for this discrepancy.