Presentation of a 57-year-old female patient with fever of unknown origin, asthenia, and weight loss for I month. History and examination were unremarkable. Blood analysis showed an important inflammatory syndrome. Other paraclinic tests were all normal. Finally, sophisticated exams (CT-scan, and FDG PET-scan) allowed the diagnosis of giant cell arteritis, confirmed by biopsy of the temporal arteries. Differential diagnosis and treatment are discussed.