Recent studies of the molecular biology of lung cancer have identified multiple abnormalities. Despite this vast cataloging of genetic lesions, the chronology of these events and those which occur early remains essentially unknown. This review summarizes the genetic abnormalities in lung cancer cells, including mutation, amplification, and overexpression of dominant protooncogenes as well as deletion and mutation of recessive oncogenes. In addition, possible candidate genes exist which may participate in the early activation events of lung cancer, and evidence for their role in the early development of cancer is discussed. These lesions may be helpful in developing strategies to screen for lung cancer.