Cigarette smoking is a well-established risk factor for postoperative complications, and preoperative smoking cessation is recommended before medical surgery. However, evidence regarding oral surgical procedures is limited, and the effects of snus, a smokeless tobacco product widely used in Sweden, on surgical outcomes remain largely unknown. The overall aim of this thesis was to address knowledge gaps regarding tobacco use and postoperative complications, with particular focus on snus. Specifically, the thesis aimed to (1) evaluate the evidence for preoperative smoking cessation in oral surgery, (2) establish a population-based cohort for studying tobacco-related health outcomes, and (3) investigate associations between snus use and postoperative complications following dental and gastrointestinal surgery. Study I was a systematic review of preoperative smoking cessation in oral surgery. Studies II–IV used a registry-based approach. Study II describes the creation of the Swedish Tobacco Cohort (SWETOC), linking tobacco exposure data from the Swedish Public Dental Service (approximately 5.5 million individuals, 1994–2023) to national health registers. Studies III and IV used SWETOC and national health registers to examine associations between snus use and postoperative complications after dental surgery (n=392,241 procedures) and gastrointestinal surgery (n=48,874 procedures), respectively, using multivariable logistic regression. The systematic review found insufficient evidence to determine the effect of preoperative smoking cessation in oral surgery. In Study III, snus use was associated with increased antibiotic prescriptions following dental surgery among women (OR 1.17, 95% CI 1.05–1.31), but not among men. As antibiotics are typically prescribed to treat or prevent infection, this finding suggests that female snus users may experience higher rates of postoperative infectious complications. In Study IV, snus use among never smokers was associated with modestly elevated risks of postoperative complications and readmission following gastrointestinal surgery, predominantly observed among men, and an increased risk of pneumonia (OR 3.09, 95% CI 1.04–7.29) compared to never tobacco users. However, the pneumonia finding should be interpreted with caution given the small number of events (n=46), as reflected by the wide confidence interval that only marginally excludes the null. Taken together, these findings suggest that the perioperative risks associated with tobacco exposure may extend beyond smoking to include smokeless tobacco products, though further research is needed to confirm these associations and clarify the mechanisms involved, including the reasons for the observed sex differences in dental surgery. This thesis illustrates how SWETOC can contribute to tobacco research and adds to emerging evidence that snus use may be associated with perioperative risks.