OBJECTIVE: To study the possible contribution of fluorodeoxyglucose (FDG)-positron emission tomography (PET) in the diagnosis of giant cell arteritis and polymyalgia rheumatica. METHODS: A consecutive case series consisting of five patients with polymyalgia rheumatica, six patients with temporal arteritis and 23 age-matched patients with other inflammatory conditions were evaluated with FDG-PET. Studies were performed before therapy with steroids was started. RESULTS: A total of 4/6 patients with giant cell arteritis and 4/5 patients with polymyalgia had increased FDG uptake in their thoracic vessels, compared to 1/23 controls (P < 0.001). Increased vascular FDG uptake in the upper legs was seen in 8/11 patients with giant cell arteritis or polymyalgia compared to 8/23 control patients (P < 0.05), and in the lower legs in 6/11 patients compared to 6/23 controls (P = not significant). CONCLUSIONS: FDG-PET scan is the first non-invasive technique which may indicate large-vessel vasculitis and which can show its extension throughout the body. It strongly suggests that polymyalgia rheumatica is a form of vasculitis.