Background: Surfer’s myelopathy is a rare complication of spinal hyperextension originally described in novice surfers. However, reports from patients practicing different activities had risen. Aim: To systematically synthesize the epidemiological and clinical evidence on acute hyperextension-induced myelopathy (“Surfer's myelopathy”) and propose new diagnostic criteria. Methods: We systematically searched four databases for all observational and case studies on the topic. We performed a narrative synthesis to propose diagnostic criteria and tested the criteria retrospectively on the included cases. A case report is also presented. Results: Forty-two articles reporting 104 cases (median age 19 years, slightly male predominance) were included. All cases reported a nontraumatic hyperextension event (58% after surfing). All of the cases presented pain of hyperacute onset. The most frequent clinical feature was bladder or bowel dysfunction (84%). The thoracic region was the most frequently affected (87%) with longitudinal involvement until the conus (67%). At discharge or follow-up, 52% partially recovered. We propose five diagnostic criteria with three levels of certainty (definite, probable, and possible): (1) nontraumatic spine hyperextension activity (in individuals with no pre-existent spinal disease); (2) hyperacute onset (with acute pain onset); (3) spinal cord injury clinic (motor, sensory, or autonomic deficit); (4) MRI findings with central spinal cord abnormalities (multiple segments); and (5) no other alternative diagnosis. We identified 88% definite and 12% probable/possible cases. Conclusion: The acute hyperextension-induced myelopathy could occur not only during surfing but also during other activities. Therefore, increased awareness and education among sports communities and general physicians are needed.