Abstract Background This study reports the incidence and prevalence of axial spondyloarthritis (axSpA) in the UK, and describes the baseline characteristics and comorbidities associated with the condition. Methods This study was conducted using the Clinical Practice Research Datalink, a large routine primary care database in the UK. Approximately 60% of contributing English primary care practices are linked to Hospital Episode Statistics (HES) secondary care data. AxSpA and relevant comorbidities were identified from Read or International Statistical Classification of Diseases and Related Health Problems-10 codes in primary care or HES datasets, respectively. The date of first axSpA diagnosis defined the index date. Patients with ≥90 days between practice registration and first axSpA diagnosis were classified as incident cases. The incidence and prevalence of axSpA were calculated annually from 2003-2017 for the UK as a whole, each constituent nation and English practices linked to HES data, to maximise case ascertainment. Comorbidities occurring prior to the index date (inclusive) were reported and compared with non-axSpA patients matched for age, sex, primary care practice and concurrent practice registration. Results Overall, 20,199 axSpA patients were identified, of whom 8,387 (41.5%) were classified as incident cases. Of the incident cases, 2,600 (31.0%) were female. Mean age at first diagnosis was 45.5 years (standard deviation [SD]: 17.2), mean body mass index was 27.2 kg/m2 (SD: 5.9) and 2,481 (29.6%) patients were current smokers. In 2017, the incidence of axSpA was 8.0 per 100,000 person-years and the prevalence was 15.8 per 10,000 population, an increase from 12.7 per 10,000 population in 2003. For patients from English practices linked to HES data, the incidence was 10.8 per 100,000 person-years and the prevalence was 17.5 per 10,000 population. 8,385 (∼100.0%) axSpA patients could be matched to non-axSpA controls. At baseline, all selected comorbidities were significantly increased in axSpA cases vs controls (Table). Conclusion This study reports an increasing prevalence of axSpA over the study period and higher rates of specific comorbidities in patients with axSpA vs matched controls. Caveats related to routine database studies, including secular changes in case ascertainment and observation bias, should be considered when interpreting these results. Disclosures C.L.I. Morgan: Other; Employee of: Pharmatelligence. A. White: Shareholder/stock ownership; Novartis. Other; Employee of: Novartis. M. Tomlinson: Consultancies; Novartis. A. Scott: Consultancies; Novartis. H. Tian: Other; Employee of: Novartis.