To identify factors associated with fibromyalgia (FM) development and recovery in patients with axial spondyloarthritis (axSpA).The British Society of Rheumatology Biologics Register (BSRBR-AS) recruited patients with axSpA from 83 centres, in a prospective study. FM was diagnosed using the self-reported Fibromyalgia Survey Diagnostic Criteria (FM-criteria) from 2015. Measures of axSpA disease activity and clinical findings were recorded at regular intervals. We identified predictors for FM development and recovery between yearly visits using uni- and multivariable logistic regression models.Eight hundred and one participants, 247 (30.8%) female, had two or more visits and were eligible for inclusion. 686 participants did not have FM at baseline, of whom 45 had developed FM at follow-up. 115 participants had FM at baseline, of whom 77 had recovered at follow-up. High baseline Bath Ankylosing Disease activity Index (OR 1.27, 95% CI 1.08-1.49) and Widespread pain index (WPI) (OR 1.14, 95% CI 1.02-1.28) were significantly associated withFM development in the final multivariable model. Low baseline Bath Ankylosing Function Index (OR 0.68, 95% CI 0.53-0.86), WPI (OR 0.84, 95% CI 0.720 to 0.97) and starting a tumour necrosis factor (TNF) inhibitor(OR 3.86, 95% CI 1.54-9.71) were significantly associated with FM recovery.High levels of disease activity and presence of widespread pain is associated with the development of FM in patients with axSpA, while low levels of the same variables and starting a TNF-inhibitor are associated with recovery from FM. The presence of co-morbid FM should be considered in patients with persistent high axSpA disease activity and wide spread pain.