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Giant cell arteritis (GCA) is the most common vasculitis in adults aged ≥ 50 years in Europe. Recently, colour Doppler ultrasonography (CDS) and positron emission tomography-computed tomography (PET/CT) have improved the diagnostic sensitivity. The aim of our study was to determine the incidence of GCA in a well-defined Slovenian region, supported by the temporal artery (TA) biopsy (TAB) or CDS or PET/CT. This prospective study was conducted at the University Medical Centre Ljubljana, the only secondary/tertiary centre in the region, serving a population of 323,297 residents aged ≥ 50 years. Patients with suspected GCA are referred either to the Department of Rheumatology, or in case of severe visual disturbances, to the Department of Ophthalmology. We included all GCA cases diagnosed between 1 January 2012 and 31 December 2017. We diagnosed cranial GCA (c-GCA) using the American College of Rheumatology (ACR) 1990 classification criteria and a positive TAB or TA-CDS. Large vessel GCA (lv-GCA) was diagnosed using CDS or PET/CT. During the 6-year observation, we identified 169 incipient GCA cases (66.3% female, median (IQR) age of 75.1 (68.6-80.0) years). Forty-two (24.8%) patients had lv-GCA, and the others had c-GCA. The estimated annual incidence rates of GCA were overall 8.7 (95% CI 7.5-10.1), c-GCA 6.5 (95% CI 5.5-7.8) and lv-GCA 2.2 (95%CI 1.6-2.9) per 100,000 aged ≥ 50 years. GCA is the most common vasculitis in adults aged ≥ 50 years, with an annual incidence rate of 8.7 per 100,000.