Objectives: The aim of the study is to examine the association of ANCA levels with disease activity and prognosis and to determine the significance of ANCA as potential biomarkers in monitoring disease activity and selecting appropriate ANCA-associated vasculitis treatment. Study design: Cross-sectional study with historical data. Participants and methods: The study included patients of the Department of Rheumatology, Clinical Immunology and Allergology of the Clinical Hospital Center Osijek with a diagnosis of ANCA-associated vasculitis in the period from 31st December 2009 to 31st December 2019. The values of pANCA and cANCA were determined by multiplex technology on the Luminex® device. The erythrocyte sedimentation rate was measured on the iSED Alcor Scientific automated device and CRP values were determined on the Beckman Coulter AU680 automated analyzer. Descriptive statistical analysis of the gained results was performed. Results: Among the examined patients, the most common diagnosis was granulomatosis with polyangiitis and the disease most often affected the kidneys and lungs. The most common comorbidities were arterial hypertension, anemia and renal failure. In terms of therapy, glucocorticoids were the most common, followed by azathioprine and cyclophosphamide. Significantly lower values of pANCA and cANCA, erythrocyte sedimentation rate and C-reactive protein were measured one year after diagnosis. Depending on the treatment outcome, 2/18 patients died, 9/18 patients had remission, 4/18 patients had stable disease and 3/18 patients had relapses. Conclusion: The increase in the ANCA titer is not sufficiently sensitive or specific predictor of relapse. However, serial measurement of PR3-ANCA could be useful in predicting severe relapses in patients with renal involvement and alveolar haemorrhage. It is recommended to perform more frequent structured clinical evaluations rather than to change therapy solely based on the ANCA determination.