Advances and integration of information and communication technologies into healthcare systems offer new opportunities to improve public health worldwide. In Sweden, there are already unique possibilities for epidemiological research from registers because of a long tradition of centralized data collection into population-based registers and their allowance for linkage. The growing efficiency of automated digital storage provides growing volumes of archived data that increases the potential of analyses further. The purpose of this thesis can be divided into two parallel themes: illustrations and discussions of the use and usefulness of population-based registers on the one hand, and specific research questions in epidemiology and healthcare research on the other. The research questions are addressed in separate papers. From the Swedish Cancer Registry, 25 years of incidence data on testicular cancer was extracted for a large cohort. Record linkage to survey data on serum cholesterol showed a highly significant positive association, suggesting that elevated serum cholesterol concentration is a risk factor for testicular cancer. Since the finding is the first of its kind and because of wide confidence intervals further studies are needed to confirm the association. Östergötland County council’s administra-tive database (the Care Data Warehouse in Östergötland (CDWÖ)) provided data for preva-lence estimations of four common chronic diseases. The prevalence rate agreed very well with previous estimates for diabetes and fairly well with those for asthma. For hypertension and chronic obstructive pulmonary disease, the observed rates were lower than previous prevalence estimates. Data on several consecutive years covering all healthcare levels are needed to achieve valid prevalence estimates. CDWÖ data was also used to analyse the impact of diabetes on the prevalence of ischemic heart disease. Women had higher diabetes/non-diabetes prevalence rate ratios across all ages. The relative gender difference remained up to the age of 65 years and thereafter decreased considerably. The age-specific direct healthcare cost of diabetes was explored using data from the CDWÖ, the county council’s Cost Per Patient database and the Swedish Prescribed Drug Register. The cost per patient and the relative magnitude of different cost components varied considerably by age, which is important to consider in the future planning of diabetes management. The Cancer Registry was established mainly as a basis for epidemiological surveillance and research, exemplified in this thesis by a study on testicular cancer. In contrast, the newly established and planned healthcare databases in different Swedish counties are mainly for managerial purposes. As is shown in this thesis, these new databases may also be used to address problems in epidemiology and healthcare research
