The cigarette-smoking behavior of 840 patients with resected Stage I non-small cell lung cancer was analyzed prospectively for up to four years following diagnosis. Lung cancer patients were heavier smokers at diagnosis than other cancer patients and the general population. At one year, only 16.8 percent of the 317 current smokers at baseline, who were followed for two years or longer, continued to smoke, while 83.2 percent of patients either quit permanently (53.0 percent) or for some time period (30.2 percent). By two years, permanent cessation stabilized at over 40 percent; however, the prevalence of continuing smoking decreased through all periods of follow-up. Subjects who tried to quit or did quit permanently were more likely to be female and healthier than continuous smokers.