There have been no target molecules that have enabled us to diagnose lung cancer with high sensitivity and specificity even in its early clinical stages. A molecule termed novel oncogene with kinase-domain (NOK) was recently reported as a receptor protein tyrosine kinase that is expressed in some cancer cell lines and causes the transformation and progressive proliferation of normal cells. Therefore, NOK could be a possible candidate for a diagnostic marker for human cancers. We examined here, the degree of NOK mRNA expression in lung cancer tissues and compared it to that in non-cancerous tissues. More than 60% of non-cancerous samples (8/13) showed undetectable levels of mRNA. In contrast, NOK mRNA was detected in 97.6% (40/41) of lung cancer tissues, resulting in a sensitivity of 80.5% and a specificity of 92.3% that was estimated using the cutoff obtained from receiver operating characteristic curve analysis. Further, NOK mRNA expression was found to be elevated in 92.3% (12/13) of cancerous tissues when paired cancerous and non-cancerous tissues from identical patients were compared. There were no obvious correlations between clinicopathological factors and NOK mRNA expression; however, NOK mRNA was highly expressed even at the early clinical stages of the cancer. These results suggest that NOK mRNA might be a new tool to support the diagnosis of lung cancers, irrespective of the clinical stages.