The Swedish cause of death register is a high-quality, nearly complete record of all deaths in Sweden since 1952. Initially created for official statistics, it has become a crucial data source for medical research due to its linkability with other national registers on social and health factors. The register's origins date back to 1749, with the first systematic collection of cause-of-death data starting in 1751. The Swedish National Board of Health and Welfare has been responsible for the register since 1994, and it is electronically available for research from 1952 onwards. The register uses the international version of the International Statistical Classification of Diseases (ICD) for coding, ensuring comparability with other countries. Death certification involves two stages: notification to the Swedish Tax Agency and a medical death certificate submitted to the National Board of Health and Welfare. The underlying cause of death is defined as the primary factor leading directly to death, and the process is complex, involving separation of contributing and underlying causes. Forensic death investigations are mandatory for unnatural deaths, unclear identities, suspected malpractice, and obscure cases, with a high autopsy rate. The register includes deaths of non-residents who die in Sweden and residents who die abroad. Completeness is high, with 96% of individuals having a specific underlying cause of death recorded, though a small proportion lacks an underlying cause. Quality is influenced by the accuracy of death certificates and the coding practices of the National Board of Health and Welfare. Key strengths include long-term data availability and high-quality data through sophisticated coding software. Weaknesses include occasional missing or incorrect personal identity numbers and a lack of recent quality checks. The main causes of death vary by age and sex, with suicide and accidents being more common at younger ages, while cancer and cardiovascular diseases become more significant with age. Over time, there has been a decrease in cardiovascular disease deaths and vehicle accidents, and an increase in cancer deaths, particularly lung cancer in women.The Swedish cause of death register is a high-quality, nearly complete record of all deaths in Sweden since 1952. Initially created for official statistics, it has become a crucial data source for medical research due to its linkability with other national registers on social and health factors. The register's origins date back to 1749, with the first systematic collection of cause-of-death data starting in 1751. The Swedish National Board of Health and Welfare has been responsible for the register since 1994, and it is electronically available for research from 1952 onwards. The register uses the international version of the International Statistical Classification of Diseases (ICD) for coding, ensuring comparability with other countries. Death certification involves two stages: notification to the Swedish Tax Agency and a medical death certificate submitted to the National Board of Health and Welfare. The underlying cause of death is defined as the primary factor leading directly to death, and the process is complex, involving separation of contributing and underlying causes. Forensic death investigations are mandatory for unnatural deaths, unclear identities, suspected malpractice, and obscure cases, with a high autopsy rate. The register includes deaths of non-residents who die in Sweden and residents who die abroad. Completeness is high, with 96% of individuals having a specific underlying cause of death recorded, though a small proportion lacks an underlying cause. Quality is influenced by the accuracy of death certificates and the coding practices of the National Board of Health and Welfare. Key strengths include long-term data availability and high-quality data through sophisticated coding software. Weaknesses include occasional missing or incorrect personal identity numbers and a lack of recent quality checks. The main causes of death vary by age and sex, with suicide and accidents being more common at younger ages, while cancer and cardiovascular diseases become more significant with age. Over time, there has been a decrease in cardiovascular disease deaths and vehicle accidents, and an increase in cancer deaths, particularly lung cancer in women.