The Swedish National Inpatient Register (IPR), also known as the Hospital Discharge Register, is a key source of data for research. Established in 1964, the IPR covers most inpatient hospital discharges in Sweden, with over 99% of somatic and psychiatric discharges recorded. It has been validated to have a high validity rate for most diagnoses, with positive predictive values (PPVs) ranging from 85-95%. The IPR is part of the National Patient Register and uses the ICD classification system. It has complete national coverage since 1987 and is linked to the personal identity number (PIN) of patients. The IPR is used for large-scale population-based research, though other registers like the Swedish Cancer Register may be more suitable for certain areas. The IPR includes variables such as patient data, caregiver data, administrative data, and medical data. It has been validated through multiple studies, showing high sensitivity for many diagnoses but lower for others like hypertension and lipid disorders. The IPR is a valuable resource for epidemiological research, with high PPV for most diagnoses. However, some diagnoses may have lower sensitivity, and additional variables could improve its utility. The IPR is also used for administrative and financial purposes, and its data are used for healthcare planning and management. Despite its strengths, the IPR has limitations, including potential underreporting of certain conditions and the need for additional variables to enhance its value. Overall, the IPR is a reliable and important tool for health research in Sweden.The Swedish National Inpatient Register (IPR), also known as the Hospital Discharge Register, is a key source of data for research. Established in 1964, the IPR covers most inpatient hospital discharges in Sweden, with over 99% of somatic and psychiatric discharges recorded. It has been validated to have a high validity rate for most diagnoses, with positive predictive values (PPVs) ranging from 85-95%. The IPR is part of the National Patient Register and uses the ICD classification system. It has complete national coverage since 1987 and is linked to the personal identity number (PIN) of patients. The IPR is used for large-scale population-based research, though other registers like the Swedish Cancer Register may be more suitable for certain areas. The IPR includes variables such as patient data, caregiver data, administrative data, and medical data. It has been validated through multiple studies, showing high sensitivity for many diagnoses but lower for others like hypertension and lipid disorders. The IPR is a valuable resource for epidemiological research, with high PPV for most diagnoses. However, some diagnoses may have lower sensitivity, and additional variables could improve its utility. The IPR is also used for administrative and financial purposes, and its data are used for healthcare planning and management. Despite its strengths, the IPR has limitations, including potential underreporting of certain conditions and the need for additional variables to enhance its value. Overall, the IPR is a reliable and important tool for health research in Sweden.