Metastin, the product of the KISS-1 gene, seems to represent a strong suppressant of metastasis for some types of cancer. The aim of this study is to explore whether circulating levels of metastin could be used as a marker for the metastatic potential of non-small cell lung cancer (NSCLC) as well as a diagnostic marker in NSCLC patients. The possible correlation between metastin and leptin circulating levels was also evaluated. Fasting serum levels of metastin and leptin were determined in 96 NSCLC patients at diagnosis (76 with metastatic disease and 21 with locally advanced disease) and 49 healthy volunteers using commercial available ELISA. Serum metastin levels presented no differences between NSCLC patients and healthy volunteers (1.18 ± 0.98 vs. 1.17 ± 0.39 ng/ml, P = 0.979) as well as between patients with metastatic and locally advanced disease (1.17 ± 1.05 vs. 1.21 ± 0.64 ng/ml, P = 0.872). There was no statistically significant correlation between circulating metastin and leptin levels in NSCLC patients and patients with locally advanced and metastatic disease. This study shows a lack of direct involvement of metastin in the diagnosis and metastatic potential of NSCLC.