Viet Nam had the highest reported male smoking prevalence rate (72.8-74.3%) in the world in the 1990s. Production of tobacco products was about 0.44 kg or 600 cigarettes per capita per year in 1994 for domestic use. Population-attributable risk per cent of lung cancer due to smoking was about 69.7%. Males in the south have a lower reported smoking prevalence rate (OR=0.7) and a significant lower incidence rate of lung cancer, age-standardized-incidence-rate per 100,000 (ASR) 33.1 vs 24.6 when compared to males in the north. Incidence rates of lung cancer significantly declined in Hanoi (ASR 34.9-33.1 and 6.3-5.8) and Ho Chi Minh City (ASR 24.6-23.7 and 6.8-5.6) between 1991-1997 and at the national level between 1990-2000 (ASR 30.4-30.1 and 6.7-6.6) in males and females, respectively. This decline in incidence rate of lung cancer resulted from the great achievements of the National Tobacco Control Program over about a 10-year period from 1989 to help people stop smoking. The present finding should stimulate further primary cancer prevention efforts in developing countries, including Viet Nam. It also suggests that the method applied to translate scientific evidence of smoking harm to people and into health policy, is a useful tool to drive people's attitude to stop smoking and remove its human carcinogens from our society.