PURPOSE: To examine the determinants of smoking behavior among participants in the Childhood Cancer Survivors Study (CCSS). METHODS: This retrospective cohort survey study was conducted among 9,709 childhood cancer survivors. Main outcomes included smoking initiation and cessation. RESULTS: Twenty-eight percent of patients reported ever smoking and 17% reported being current smokers. Standardized to United States population rates, the observed to expected (O/E) ratios and corresponding 95% confidence limits (95% CL) of cigarette smoking were 0.72 (95% CL, 0.69, 0.75) among all survivors and 0.71 (95% CL, 0.68 to 0.74) and 0.81 (95% CL, 0.70, 0.93) among whites and nonwhites, respectively. Significantly lower O/E ratios were present among both males (O/E, 0.73) and females (O/E, 0.70). Factors independently associated with a statistically significant relative risk of smoking initiation included older age at cancer diagnosis, lower household income, less education, not having had pulmonary-related cancer treatment, and not having had brain radiation. Blacks were less likely to start smoking. Survivors who smoked were significantly more likely to quit (O/E, 1.22; 95% CL, 1.15, 1.30). Among ever-smokers, factors associated with the likelihood of being a current smoker included age less than 13 years at smoking initiation, less education, and having had brain radiation; those age less than 3 years at cancer diagnosis were significantly more likely to be ex-smokers. CONCLUSIONS: Although survivors in the CCSS cohort seem to be smoking at rates below the general population, interventions are needed to prevent smoking initiation and promote cessation in this distinct population.