The occurrence of lung cancer is associated with smoking, which exposes smokers to a series of carcinogenic chemicals. CYP (cytochrome P450) usually metabolizes carcinogens to their inactive derivatives, but occasionally convert the chemicals to more potent carcinogens. In addition to the metabolism of carcinogenic compounds, CYP also participates in the activation and/or inactivation of anti-carcinogenic agents, suggesting that the local CYP expression in lung cancer and surrounding tissues could be an important determinant of efficacy of anticancer drugs. Furthermore, CYP19 (aromatase), estrogen synthase P450, expressed in more than 80 percent of non-small cell lung cancers. It suggests an association between estrogens and cancer development, which makes aromatase an attractive therapeutic target for the treatment of lung cancer. 1alpha,25-Dihydroxyvitamin D3 has an inhibitory effect on the proliferation of cancer tissues, and is converted to its inactive 24-hydroxylated derivatives by CYP24, which is frequently expressed in lung cancer tissues. Therefore, understanding the CYP expression in tumor tissues is important in developing better therapies for lung cancer, and may lead us to standardized, tailor-made therapies for individuals.