Rationale:Giant cell arteritis (GCA) is an autoimmune vasculitis that affects large and medium-sized blood vessels. The mRNA vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) has been associated with the development of immune-mediated diseases. In this article, we present a case of GCA that developed after vaccination against SARS-CoV2.Patient concerns:A 77-year-old man developed fever, general fatigue, and headache 1 day after the third dose of vaccination against SARS-CoV2. Nodular swelling and tenderness of the bilateral temporal arteries were observed.Diagnoses:Although right temporal artery biopsies were negative, the patient was diagnosed with GCA based on criteria established by the American College of Rheumatology for the classification of GCA.Interventions:The patient received methylprednisolone 1000 mg for 3 days. This was followed by prednisolone 1 mg/kg/d, which was decreased by 10 mg every week to 30 mg. From day 16 of hospitalization, the patient received tocilizumab 162 mg/wk every other week.Outcomes:There was no occurrence of acute side effects. After 38 days of treatment, the condition improved and the patient was discharged from the hospital; as stated above, the dose of prednisolone was tapered to 30 mg/d.Lessons:We experienced a case of GCA that occurred immediately after vaccination against SARS-CoV2 with an mRNA vaccine. Early signs of GCA include fever, fatigue, and headache, and often resemble those noted after vaccination against SARS-CoV2. The potential presence of GCA should be determined in individuals with persistent fever and headache after vaccination against SARS-CoV2.