Arterial pseudoaneurysms can develop secondary to a vessel injury, for example, an arterial line installation. We present a case of an 18-year-old female with mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes syndrome who developed left radial artery and right brachial artery pseudoaneurysms secondary to arterial line placement and repeated blood draws, respectively. The ultrasonographic features of pulsating mass in connection with an artery and the yin-yang sign, combined with the patient's history, allowed accurate diagnosis. She was referred to vascular surgery for definitive treatment.