Ulnar artery aneurysms are an exceedingly rare entity in the pediatric population and have no consistent etiologic mechanism. We present the case of a 15-year-old male with a multilocular ulnar artery aneurysm in the setting of no antecedent history of trauma, no identifiable connective tissue disorders, and no other apparent etiological factors. Furthermore, the patient's arterial palmar arch system was absent. The aneurysm was resected, and arterial reconstruction was successfully performed via open surgical approach with cephalic vein interposition graft. We believe this treatment modality should be considered as the primary approach in all of these pediatric cases in consideration of the possible pitfalls of less comprehensive measures.