Peripheral arterial aneurysms in children are uncommon. We report a 6-year-old boy who developed a right posterior tibial artery aneurysm with symptoms including pain and pulsatile tenderness. His genetic testing revealed a SMAD3 mutation, a condition associated with familial aortic aneurysm, early-onset of osteoarthritis, and peripheral aneurysms. The posterior tibial artery aneurysm was treated with surgical resection and primary anastomosis. The patient remained free of symptoms or aneurysm recurrence in his tibial artery 2 years later. This represents the first reported case of pediatric tibial artery aneurysm linked to a SMAD3 mutation.