Lateral medullary syndrome is rare in pediatrics. It is characterized by neurological deficits due to an ischemic lesion in the lateral medulla. The authors describe a 17-year-old boy who developed lateral medullary syndrome in the context of a hyperflexion neck injury while diving in shallow water with traumatic vascular injury. He had "crossed" neurological deficits above and below the neck. His magnetic resonance angiography showed intra- and extracranial left vertebral artery occlusion and his magnetic resonance imaging showed signal abnormality involving the left lateral medulla and inferomedial cerebellum in keeping with an infarct secondary to left vertebral artery and left posterior inferior cerebellar artery occlusion. Good neurological recovery was observed on heparin therapy started after surgical treatment of traumatic injury. To our knowledge, this is the first reported case of lateral medullary syndrome in a pediatric population related to a flexion neck injury. The authors emphasize the importance of a high level of suspicion for accurate diagnosis.