Acute thrombosis of the SMV, initially described in 1894, is a rare cause of intestinal ischemia, with an incidence of 1.8 per 100,000 person-years.[1] Potential causes of thrombophilia or hypercoagulable state may include myeloproliferative disease, antiphospholipid syndrome, factor V Leiden mutation, paroxysmal nocturnal hemoglobinuria, hereditary deficiencies of protein S, protein C, and antithrombin, hyperhomocysteinemia, and oral contraceptive use. The gene discussed is PROS1; the disease is paroxysmal nocturnal hemoglobinuria.