Objective: Chronic fatigue is a major burden of disease in patients with ANCA-Associated Vasculitis (AAV) which results in a decreased quality of life. The prevalence of fatigue in AAV is, however, unknown. The aim of our study is to evaluate the presence of chronic fatigue in patients with a diagnosis of AAV i.e., granulomatosis with polyangiitis, eosinophilic granulomatosis with polyangiitis or microscopic polyangiitis, and to identify potential clinical and biopsychosocial determinants. Methods: 59 participants included in our study completed the validated DePaul Symptom Questionnaire (DSQ). Patients were labelled with “Myalgic Encephalomyelitis (ME)/Chronic Fatigue Syndrome (CFS)” when they fulfilled the Canadian Consensus Criteria for ME/CFS. Disease activity was scored using Birmingham Vasculitis Activity (BVAS), whereas the Vasculitis damage index (VDI) was used to evaluate damage. Mental comorbidities where analyzed to understand potential biopsychosocial factors related to chronic fatigue. To assess anxiety and depression we used the Hospital Anxiety and Depression scale (HADS). We also used the Cognitive Failure Questionnaire (CFQ) to estimate the frequency of cognitive failure. Sleep quality was assessed using The Pittsburgh Sleep Quality Index (PSQI). Statistical analysis was carried out using Fischer’s exact test. Results: We found that 32/59 (54%) of AAV patients fulfilled the case definition for ME/CFS. There was no relationship between the presence of ME/CFS and BVAS (p=0.5), VDI (p=0.78), sleep disorders (p=0.8), depression (p=0.09) or C-reactive protein (p=0.2399) in our study population. However, a substantial statistically significant correlation was present in patients with AAV suffering from ME/CFS, cognitive failure (p=0.004) and/ or anxiety (p= <0.001). Conclusion: Chronic fatigue affects AAV patient’s mental wellbeing. From our analysis we conclude that chronic fatigue, cognitive failure and/or anxiety co-occur independently of vasculitis disease activity. We postulate that therapies aimed at improving anxiety may be utilized as adjunct agents for patients with AAV suffering from Chronic fatigue. Disclosure: Dutch Kidney Foundation (17PhD01) Arthritis Society (19-0558)