The Swedish personal identity number (PIN) is a unique identifier used in healthcare and medical research. It is a ten-digit number assigned to individuals residing in Sweden since 1947, with the first six digits representing the date of birth and the last four digits serving as a check digit. The PIN is crucial for linking medical registers and ensuring accurate data collection in healthcare. It is also used for population statistics, taxation, education, and social security. However, there are ethical concerns regarding its use, including the potential for incorrect or reused PINs, which can lead to data inaccuracies. The PIN system has been reviewed for its structure and potential pitfalls, with the National Tax Board responsible for maintaining it. The PIN is essential for efficient healthcare management and research, allowing for comprehensive data analysis. Despite the risks, the PIN is considered a valuable tool for healthcare and research in Sweden. The use of the PIN in medical research is supported by the fact that it enables accurate data linkage and is widely used in public administration. Ethical considerations include the need for informed consent, but the authors argue that it is not necessary for large-scale research due to the benefits it provides to both patients and society. The PIN system is also used in other Nordic countries, with similar structures. Overall, the PIN plays a vital role in Swedish healthcare and research, despite the challenges and ethical considerations associated with its use.The Swedish personal identity number (PIN) is a unique identifier used in healthcare and medical research. It is a ten-digit number assigned to individuals residing in Sweden since 1947, with the first six digits representing the date of birth and the last four digits serving as a check digit. The PIN is crucial for linking medical registers and ensuring accurate data collection in healthcare. It is also used for population statistics, taxation, education, and social security. However, there are ethical concerns regarding its use, including the potential for incorrect or reused PINs, which can lead to data inaccuracies. The PIN system has been reviewed for its structure and potential pitfalls, with the National Tax Board responsible for maintaining it. The PIN is essential for efficient healthcare management and research, allowing for comprehensive data analysis. Despite the risks, the PIN is considered a valuable tool for healthcare and research in Sweden. The use of the PIN in medical research is supported by the fact that it enables accurate data linkage and is widely used in public administration. Ethical considerations include the need for informed consent, but the authors argue that it is not necessary for large-scale research due to the benefits it provides to both patients and society. The PIN system is also used in other Nordic countries, with similar structures. Overall, the PIN plays a vital role in Swedish healthcare and research, despite the challenges and ethical considerations associated with its use.