The hypothenar hammer syndrome describes a constellation of symptoms resulting from repetitive trauma to the hypothenar eminence, often due to the use of the hand as a hammer. Sequelae of this syndrome include both true and false aneurysms, as well as thrombosis of the ulnar artery due to its vulnerability to blunt trauma as it exits Guyon's canal. Although this is a relatively well-documented phenomenon, an extensive review of the literature revealed that no cases have been described involving a patient with hemophilia. The present case describes a 46-year-old farmer with factor IX deficiency (hemophilia B) presenting with a 5 cm x 7 cm pseudoaneurysm of the ulnar artery of the right hand.