A 10-month-old boy with a known diagnosis of tuberous sclerosis presented with axillary and brachial masses. Cross-sectional imaging with computed tomography, magnetic resonance, and ultrasound demonstrated unsuspected aneurysms of the axillary and brachial arteries. The results of these studies significantly changed the preoperative planning for this patient, who was scheduled for a biopsy of a presumed soft-tissue tumor. To our knowledge, this is the first description of the cross-sectional imaging findings in the extremity peripheral vascular manifestation of tuberous sclerosis; it has only been previously described on angiography in one case. The rare association of peripheral arterial aneurysms with tuberous sclerosis is important to recognize not only for clinical diagnosis but also for appropriate surgical treatment and genetic counseling.