BackgroundThe British Lung Foundation (BLF) has previously estimated that there are 2.2 million people in the UK who have symptoms, but no diagnosis, of chronic obstructive pulmonary disease (COPD).AimTo investigate the proportion of patients with a missed COPD diagnosis among those with COPD as the cause of death on their death certificate, and how this has changed over a period of 17 years (2000–2017).Design & settingClinical Practice Research Datalink (CPRD) Aurum and GOLD primary care data were linked with Office for National Statistics (ONS) mortality data and Hospital Episode Statistics (HES) data. Adults who died between 2000 and 2017 with COPD as their main cause of death were included.MethodUsing a range of diagnostic COPD criteria, the proportion of patients with a missed COPD diagnosis was estimated, and the demographic and clinical characteristics of patients with and without prior COPD diagnosis were described, using a mixed-effect logistic regression model.ResultsDepending on the COPD definition used, between 96% and 27% of the 78 621 patients included received a diagnosis of COPD before death. Using presence of a COPD Read or SNOMED CT code and performed spirometry as a main definition, just over half of the patients (52%) had received a COPD diagnosis overall, with a proportion of those who did not decreasing from 91% in 2000 to 31% in 2017 (P_trend<0.001).ConclusionThe proportion of people with COPD-recorded death and who had received a diagnosis of COPD has improved (increased) over time, and currently represents the majority of them. This suggests that few patients are now being missed.