The authors report the case of a 5-year-old female with right-sided hemiparesis and aphasia secondary to moyamoya disease, who had previously undergone staged bilateral encephaloduroarteriosynangiosis procedures. A subsequent ground-level fall caused an acute traumatic subdural hematoma with mass effect and neurological decline. She underwent emergency hematoma evacuation and decompressive craniectomy, which required interruption of the superficial temporal artery that had been used for indirect bypass, followed later by autologous cranioplasty. There were no acute or long-term ischemic events related to the occurrence or treatment of the traumatic hematoma. Follow-up angiography revealed extensive spontaneous vascular collateralization in the field of the decompressive craniectomy and cranioplasty. The patient returned to her pre-injury neurological baseline.