OBJECTIVES: We calculated regional and sex- and age-specific smoking prevalence estimates worldwide in 1995. METHODS: Sex-specific smoking prevalence data from studies in 139 countries and age distribution data from 7 studies were analyzed. RESULTS: Globally, 29% of persons aged 15 years or older were regular smokers in 1995. Four fifths of the world's 1.1 billion smokers lived in low- or middle-income countries. East Asian countries accounted for a disproportionately high percentage (38%) of the world's smokers. Males accounted for four fifths of all smokers, and prevalence among males and females was highest among those aged 30 to 49 years (34%). CONCLUSIONS: Future decades will see dramatic increases in tobacco-attributable deaths in low- and middle-income regions. Although much of this excess mortality can be prevented if smokers stop smoking, quitting remains rare in low- and middle-income countries.