Bone metastases often appear in advanced stages of lung cancer. They are the result of modulation of bone metabolism by tumor cells that migrated into bone microenvironment and degraded bone organic matrix. Measurement of C-terminal telopeptide of type I collagen (ICTP) in the serum of subjects with lung cancer with and without bone metastases and healthy population is the way to explore bone resorption. In 343 subjects included in this research ICTP level was significantly higher in the bone metastasis than other two groups. The existence of pathologic fracture significantly increased ICTP level. ICTP showed sensitivity of 66.0% in bone metastases at 95.0% specificity in lung cancer stages IA and IB. ICTP is a good diagnostic marker in detection of bone metastasis of lung cancer. Its level can distinguish lung cancer with and without bone involvement and can be used as an addition to standard techniques used in diagnostics of bone metastasis.