Vaccine-induced immune thrombosis and thrombocytopenia (VITT) is a new syndrome, which has emerged after introduction of the adenovirus vector-based COVID-19 vaccines ChAdOx1 nCoV-19 og Ad26.COV2-SVITT is characterised by venous thrombosis at unusual, and often multiple localisations, especially including cerebral venous sinus thrombosis. Besides, bleeding manifestations often occur. Biochemically, VITT is characterised by thrombocytopaenia and elevated fibrin d-dimer. VITT is a rapidly progressing and potentially life-threatening syndrome where rapid diagnosis and treatment are essential as argued in this review.