Background Balance in the coagulation system is essential for human survival. When this balance is disturbed, both an increased tendency to bleed and an increased risk of thrombosis-related events can occur, leading to illness, suffering and death. Even small haemorrhages and thromboses can lead to major damage if sensitive areas such as the central nervous system are affected. About 1 in 1000 people suffer from deep vein thrombosis or pulmonary embolism each year and various conditions with thrombosis or risk of thrombosis are treated with anticoagulants. Such treatment always carries a risk of bleeding complications. About 1-2% of patients treated with anticoagulants suffer serious bleeding events each year that require hospitalisation. With 25% of people aged 65 and over taking anticoagulants, this results in both significant suffering and a considerable cost to society. Purpose The aim of the project is to identify the risk of thrombosis-related events or bleeding complications leading to emergency hospitalisation, admission to hospital or death in people taking anticoagulants, whether this risk is increased in connection with surgical procedures in dentistry or health care, and whether there are differences in risk between different anticoagulants. The following questions are relevant for the project: - What is the risk of bleeding complications in patients taking anticoagulants? - What is the risk of thrombosis-related events in patients taking anticoagulants? - How do anticoagulants affect the risk of bleeding complications in patients undergoing dental or medical surgery? - How do anticoagulants affect the risk of thrombosis-related events in patients undergoing dental or medical surgery? - How does adjusting current anticoagulant medication affect the risk of bleeding complications associated with dental or medical surgical procedures? - How does adjusting current anticoagulant medication affect the risk of thrombosis-related events associated with dental or medical surgical procedures? Material & Methods The research material consists of register data and medical record data. Data collection includes ordering register extracts from Statistics Sweden and from the National Board of Health and Welfare, searches in regional health registers and contact with dental clinics and health care institutions for the collection of data from patient records. Trial 1 and 2 are cohort studies to determine whether the risk of thrombosis-related events or bleeding complications leading to emergency hospitalisation, inpatient hospitalisation or death is increased in people taking anticoagulants compared to people not taking anticoagulants, both in general and in connection with dental or medical surgical procedures. Trial 3 is a case-crossover study and trial 4 is a nested case-control study. The aim of these studies is to determine whether the risk of thrombosis-related events or bleeding complications leading to emergency hospitalisation, inpatient hospitalisation or death is higher in patients taking anticoagulants 30 days after dental or medical surgery compared to other time periods, both in general and when anticoagulants are discontinued or dose adjusted at the time of surgery.