BACKGROUND: Smoking should be particularly discouraged among survivors of childhood cancer, who are at increased risk of adverse effects of the cancer and its treatment. We examined the extent of cigarette smoking, factors associated with being a current smoker, and age at initiation of regular smoking among adult survivors of childhood cancer and compared the survivors' smoking habits with those of the general population. METHODS: We used data from the British Childhood Cancer Survivor Study (BCCSS), a population-based cohort of 17 981 individuals who were diagnosed with childhood cancer between 1940 and 1991 in Britain and had survived for at least 5 years after diagnosis. The 14 836 cohort members who were alive and aged 16 years or older up to September 2006 were eligible to receive a mailed questionnaire that ascertained smoking status and other factors. The general population data were from the 2002 General Household Survey in Britain. Logistic regression was used to investigate factors associated with being a current regular smoker and to compare the prevalence of current regular smoking in the study cohort with that in the general population. Cox regression was used to examine associations between explanatory factors and age at smoking initiation. All statistical tests were two-sided. RESULTS: Of the 10 326 childhood cancer survivors who returned completed questionnaires, 20.0% were current regular smokers and 29.8% were ever regular smokers, whereas in the comparable general population 28.1% were current regular smokers and 48.8% were ever regular smokers. Current regular smoking was more prevalent among survivors of Wilms tumor or Hodgkin lymphoma than survivors of a central nervous system (CNS) neoplasm; in those aged 10-14 years at diagnosis than 0-4 years; in those not treated with radiotherapy; in those in manual occupations; in those who were separated, widowed, or divorced; in those with lower educational attainment; and in those not currently on long-term regular hospital follow-up. Rates of smoking initiation were lower in women; in those treated with chemotherapy or radiotherapy; and in those with a third party-completed questionnaire. The rate of smoking initiation was highest among those diagnosed at 10-14 years of age. The odds ratio for being a current regular smoker among the survivors compared with the general population was 0.51 (99% confidence interval [CI] = 0.46 to 0.57). Survivors who smoked, smoked fewer cigarettes per day than smokers in the general population; the difference in the multivariable model was 1.5 fewer cigarettes per day (95% CI = 1.03 to 1.99). CONCLUSION: The prevalence of smoking varies by subgroup among adult survivors of childhood cancer in the BCCSS but is substantially less overall than that in the general population.