A case report describing thrombosis of the ulnar artery after blunt direct trauma of the hand is presented. Traumatic thrombosis of the ulnar artery is rare. An isolated direct trauma is the most frequent pathogenetic mechanism. The patient's history is of great importance for reconstruction of the accident and for insurance questions. To clarify the etiology and angiography or the new method of MRI-angiotomography is mandatory. The therapy is usually conservative, and only in selected cases (aneurysm, old thrombosis) should an operative therapy be considered.