OBJECTIVE: To report on prevalence, trends and determinants of smoke-free home policies in smokers' homes in different countries and to estimate the effects of these policies on smoking cessation. DESIGN: Two waves of the International Tobacco Control (ITC) Four Country Survey (ITC-4), a cohort survey of smokers conducted by telephone. Wave 1 was conducted in October/December 2002 with broadly representative samples of over 2000 adult (>or= 18 years) cigarette smokers in each of the following four countries: Canada, the United States, the United Kingdom, and Australia, 75% of whom were followed up at Wave 2 on average seven months later. KEY MEASURES: Levels of smoking restrictions in homes (both waves). RESULTS: Australian smokers were most likely to live in smoke-free homes and UK smokers least likely (34% v 15% at Wave 1). Levels of smoke-free homes increased between waves. Logistic regressions indicated that the main independent predictors of smokers reporting smoke-free homes or implementation of a smoke-free policy between waves included household factors such as having a child, particularly a young child, and having other non-smoking adults in the household. Positive attitudes to smoke-free public places and/or reported presence of smoke-free public places were independent predictors of having or implementing smoke-free homes, supporting a social diffusion model for smoking restrictions. Intentions to quit at Wave 1 and quitting activity between survey waves were associated with implementing bans between Waves 1 and 2. Presence of bans at Wave 1 was associated with significantly greater proportions of quit attempts, and success among those who tried at Wave 2. There was no significant interaction between the predictive models and country. CONCLUSIONS: Smoke-free public places seem to stimulate adoption of smoke-free homes, a strategy associated with both increased frequency of quit attempts, and of the success of those attempts.