Lung cancer is the leading cause of cancer death and the second most commonly diagnosed cancer (excluding skin cancer) among men and women in the United States. Although lung cancer can be caused by environmental exposures, most efforts to prevent lung cancer emphasize tobacco control because 80%-90% of lung cancers are attributed to cigarette smoking and secondhand smoke. One sentinel health consequence of tobacco use is lung cancer, and one way to measure the impact of tobacco control is by examining trends in lung cancer incidence rates, particularly among younger adults. Changes in lung cancer rates among younger adults likely reflect recent changes in risk exposure. To assess lung cancer incidence and trends among men and women by age group, CDC used data from the National Program of Cancer Registries (NPCR) and the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) program for the period 2005-2009, the most recent data available. During the study period, lung cancer incidence decreased among men in all age groups except <35 years and decreased among women aged 35-44 years and 54-64 years. Lung cancer incidence decreased more rapidly among men than among women and more rapidly among adults aged 35-44 years than among other age groups. To further reduce lung cancer incidence in the United States, proven population-based tobacco prevention and control strategies should receive sustained attention and support.