An overview of prevalence and incidence studies performed in Swedish centres is provided, showing improving coverage and methodology, notably the development in Gothenburg of the representative incidence cohort design. A common database for major Swedish centres was established in 1995, implementing the terminology of predictors from the Gothenburg cohort. By 2001, these databases were merged into the web-based national multiple sclerosis (MS) registry, which has had an ever-increasing coverage, although with still moderate data density. The registry now contains records on 13,000 Swedish patients with MS. It has the status of a national quality registry and exerts nation-wide pharmacological surveillance. In addition, it has been, and is being, used in nearly 100 scientific studies, including large epidemiological and genetic projects.