In industrialized countries, tobacco smoking is the main cause of preventable morbidity and premature deaths. Although mortality attributable to smoking has already been estimated for the population of the province of Québec, it has never been studied on a regional basis. We calculated the mortality attributable to smoking by socio-sanitary regions of the province of Québec for 10 fatal diseases positively associated with smoking. The calculations were made for the years 1984 through 1993 taking into account Canadian Census data (demographic variables), the Santé-Québec survey (prevalence of smoking), the death registry of the "Bureau de la statistique du Québec" (mortalitry data), and the American cohort of the "Cancer Prevention Study II" (relative risks). For the diseases investigated, 24,637 and 62,711 deaths were attributable to smoking for women and men respectively during the period studied, thus representing 29.4% and 51.2% of attributable percentages. There is no statistical difference between the regions, which indicates a general problem for all the province. These data again confirm the incredible impact of smoking on public health. The struggle against smoking should be a primary area for action for the benefit of all Quebecers.