 The Swedish National Inpatient Register, IPR, has been used extensively for research purposes since its launch in 1964. It is now one of the most comprehensive sources of data on hospital admissions in Sweden, with over 99% of all hospitalizations being recorded. The IPR is highly reliable for most diagnoses, with a PPV ranging from 85 to 95%, depending on the specific diagnosis. However, it should be noted that some diagnoses have lower reliability due to their low prevalence in the general population. Despite this, the IPR remains a valuable resource for epidemiological studies and population-based research. This article was authored by Kim Jong-lim, Fakding Maria, Ekbom Anders, and others.