Lung cancer accounts for most of cancer-related deaths in both men and women. Lung cancer is also associated with cigarette smoking that exposes the individual to carcinogenic chemicals. Normally, CYP enzymes (cytochrome P450s) metabolize carcinogens to inactive derivatives, however, occasionally the action of CYP enzymes leads to development of more potent carcinogens. In addition to the metabolism of carcinogenic compounds, CYP enzymes are also involved in the activation and/or inactivation of agents, which are used in the treatment of lung cancer. Therefore, the local level of CYP enzymes in lung cancer and surrounding tissues could be an important determinant in the efficacy of anticancer drugs. Furthermore, the expression of CYP19 (aromatase), estrogen synthesis P450, was found in more than 80 percent of non-small cell lung cancers. Lung cancer was also found to frequently express CYP24A1 that converts 1 alpha, 25-dihydroxyvitamin D3 to its inactive 24-hydroxylated derivatives. The understanding of the local expression of CYP enzymes in tumor tissues is important in the development of better treatment for lung cancer and a standardized treatment, tailor-made, for individual patients.