The long-term survival of individuals with trisomy 18 has improved, and the need for tracheostomy in this population has thus increased. We describe the case of a 3-year-old Japanese boy with trisomy 18 who developed a tracheoarterial fistula involving the left common carotid artery (LCCA). He underwent an emergency tracheostomy for respiratory failure secondary to pneumonia. Massive hemorrhage from the tracheostoma occurred on postoperative day 31, leading to his death. The autopsy revealed that the LCCA originated from the brachiocephalic trunk and coursed medially, forming a fistulous connection with the trachea. This case highlights the clinical importance of preoperative vascular mapping in patients with chromosomal abnormalities.