The SNMC was a large, prospective cohort set up to investigate associations between lifestyle factors and chronic diseases, including cancer, including over 43,000 participants across Sweden. Participants were invited to join the cohort and fill in a baseline questionnaire in September 1997 at the Swedish National March, a 4-day promotional and fund-raising event for the Swedish Cancer Society that took place in almost 3,600 Swedish cities and villages. Complete follow-up was attained through multiple record linkages, done approximately biannually, using the individually unique national registration numbers to ensure exact linkages.