Abstract
Recently, ustekinumab has been approved for the treatment of Crohn's disease and ulcerative colitis. Treatment is started with an intravenous induction dose, followed by a subcutaneous dosage. We present details of three patients with therapy-refractory Crohn's disease who experienced an immediate infusion reaction to intravenous administration of ustekinumab. In two of these patients a subsequent reaction to subcutaneous injections occurred. Clinical features and pathophysiology are discussed.