We report the case of a 41-year-old man presenting with hepatic vein thrombosis (Budd-Chiari syndrome) during Infliximab therapy for ankylosing spondylitis. The systematic work-up revealed paroxysmal nocturnal hemoglobinuria. One year later the patient was receiving anticoagulation therapy and was in good condition. The role of Infliximab in the development of thrombosis in this patient with rare underlying thrombophilia is discussed. We report the case of a 41-year-old man presenting with hepatic vein thrombosis (Budd-Chiari syndrome) during Infliximab therapy for ankylosing spondylitis. The systematic work-up revealed paroxysmal nocturnal hemoglobinuria. One year later the patient was receiving anticoagulation therapy and was in good condition. The role of Infliximab in the development of thrombosis in this patient with rare underlying thrombophilia is discussed.