BACKGROUND Carotid blowout syndrome (CBS) refers to rupture of the extracranial carotid artery and its branches; as a severe complication, it usually occurs after surgery or radiotherapy for malignant tumours of the head and neck. We present a case of CBS caused by chronic infection of the external carotid artery (ECA). In this case, we did not find any evidence of head and neck tumours. CASE SUMMARY A 42-year-old man was referred to the Emergency Department with a complaint of a lump found on the left side of his neck with pain and fever for 4 d. We diagnosed the condition as neck infection with abscess formation based on physical examination, routine blood examination, ultrasound examination and plain computed tomography (CT) and decided to perform emergency surgery. During the operation, 30 mL of grey and smelly pus was drained from the deep surface of the sternocleidomastoid muscle. The second day after the operation, the patient suddenly exhibited a large amount of haemoptysis and incision bleeding. The enhanced CT showed distal occlusion of the left ECA and irregular thickening of the broken ends of the artery encased in an uneven enhancement of soft tissue density. Infected ECA occlusion and rupture were considered. The patient was transferred to a vascular unit for transcatheter ECA embolization and recovered well. CONCLUSION Surgeons need to pay attention to vascular lesions caused by chronic infection that may develop into acute CBS.