BACKGROUND AND OBJECTIVES For many years Swedish men have had the world's lowest rates of smoking and smoking-related mortality. Despite these facts, a thorough analysis of tobacco use patterns in Sweden has not been performed. The purpose of this study was to examine the prevalence and interaction of cigarette smoking and use of Swedish moist snuff (snus) in the population of northern Sweden. DESIGN The study cohort of 2998 men and 3092 women aged 25-64 was derived from the northern Sweden MONICA study, consisting of population-based surveys in 1986, 1990, 1994 and 1999. Detailed information on tobacco use was used to develop prevalence data, and the prevalence ratio was used to compare rates amongst various subgroups. RESULTS Amongst men ever-tobacco use was stable in all survey years at about 65%, but the prevalence of smoking declined from 23% in 1986 to 14% in 1999, whilst snus use increased from 22% to 30%. In women the prevalence of smoking was more stable in the first three surveys (approximately 27%) but was 22% in 1999, when snus use was 6%. In all years men showed higher prevalence of ex-smoking than women. A dominant factor was a history of snus (PR = 6.18, CI = 4.96-7.70), which was more prevalent at younger ages. CONCLUSIONS The recent transition from smoking to snus use amongst men, and incipiently amongst women, in northern Sweden is remarkable and relevant to the global discussion on strategies to reduce smoking.