The purpose of this study is to validate the diagnosis of spontaneous abortion (SA) recorded in the Danish National Registry of Patients (DNRP).We randomly selected patients registered in the DNRP with a diagnosis of SA between 1980 and 2008 from hospitals in the county of North Jutland and searched for their discharge records in hospital files. We estimated positive predictive value (PPV) of the DNRP diagnosis and stratified the analysis by period (1980-1994 versus 1995-2008), hospital type (regional versus local), and International Classification of Diseases revisions (ICD-8 versus ICD-10).We could identify hospital files of 117/174 (67%) sampled registration records. Of those, the diagnosis was confirmed in 114 patients, yielding a PPV of 97.4% (95% confidence interval = 92.7%-99.5%). The PPV did not markedly vary by period, hospital type, or ICD revision. Among the three patients with available data who did not fulfill the criteria for SA, one had an induced abortion and two had threatened abortion but did not miscarry.Registration of SA in the DNRP accurately reflects the diagnoses recorded in medical charts. The DNRP is a suitable source of data on SAs for epidemiologic research.