A 11-year-old girl suffered a minor head injury during a snowball fight. She showed an abnormal behavior several hours later and consulted our hospital the next day. An acute ischemic lesion was detected in the left caudate head on CT. MRA revealed string sign in the left A1 and A2 segment. A diagnosis of posttraumatic anterior cerebral artery dissection was made. Cerebral angiography per­formed 11 days after head injury revealed occlusion of left anterior cerebral artery. The occlusion of the anterior cerebr­al artery after minor head trauma is extremely rare condition and has not reported so far.