Pseudoaneurysms occur secondary to partial disruption of the arterial wall. They are a commonly described complication of arterial injury, with penetrating injury and iatrogenic arterial catheterization being the most common etiologies in children. Many present weeks to months after the injury, and the initial vascular injury is often missed. The complications of pseudoaneurysm, which include thromboembolism, neurapraxia, and compartment syndrome, underscore the importance of early recognition and management. Definitive therapy consists of ultrasound-guided compression or resection and possible graft interposition. We describe a case of pseudoaneurysm formation in the radial artery of an adolescent girl 6weeks following a penetrating injury. The patient’s injury was complicated by sensory and motor deficits consistent with ulnar nerve compression. This case attests to the importance of adequately ruling out arterial injury in penetrating injury and close followup if the history is suggestive. In addition, a high index of suspicion is warranted to facilitate imaging of a pulsatile mass to avoid confusion of a thrombosed artery with an abscess.