Lung cancer can be detected via screening of high-risk individuals, i.e current or ex-heavy smokers, with low-dose computer tomography (LDCT) of thorax. The National Lung Screening Trial in US and the NELSON trial in Europe demonstrated reduction in lung cancer mortality with LDCT screening for lung cancer. In Hong Kong, however, there is a prominence of female never-smokers with lung cancer. There is no identifiable risk factors for non-smokers with lung cancer except family history of lung cancer. The hypothesis is that lung cancer screening for subjects with family history of lung cancer, can detect early lung cancer.