Spontaneous rupture and bleeding from the carotid artery in acute promyelocytic leukemia (APL) patients leading to pseudoaneurysm (PSA) formation has not been reported.We first successfully treated an APL patient with left intal carotid artery rupture during chemotherapy leading to PSA using ultrasound-guided thrombin injection (UGTI).A 10-year-old girl,who was diagnosed with APL,suddenly experienced left neck swelling,which expanded gradually and was not associated with pain,dizziness,palpitations,or labored breathing 2 days after the third session of chemotherapy (mitoxantrone + cytarabine) in a local hospital.She had no history of injury.