OBJECTIVE: To examine the concordance between dates of death recorded in UK primary care and national mortality records. METHODS: UK primary care data from the Clinical Practice Research Datalink were linked to Office for National Statistics (ONS) data, for 118 571 patients who died between September 2010 and September 2015. Logistic regression was used to examine factors associated with discrepancy in death dates between data sets. RESULTS: Death dates matched in 76.8% of cases with primary care dates preceding ONS date in 2.9%, and following in 20.3% of cases; 92.2% of cases differed by <2 weeks. Primary care date was >4 weeks later than ONS in 1.5% of cases and occurred more frequently with deaths categorised as 'external' (15.8% vs 0.8% for cancer), and in younger patients (15.9% vs 1% for 18-29 and 80-89 years, respectively). General practices with the greatest discrepancies (97.5th percentile) had around 200 times higher odds of recording substantially discordant dates than practices with the lowest discrepancies (2.5th percentile). CONCLUSION: Dates of death in primary care records often disagree with national records and should be treated with caution. There is marked variation between practices, and studies involving young patients, unexplained deaths and where precise date of death is important are particularly vulnerable to these issues.