Second impact syndrome is believed to be the catastrophic consequence of repeated head injury in sport. The scientific evidence to support this concept is nonexistent, and belief in the syndrome is based upon the interpretation of anecdotal cases more often than not, lacking sufficient clinical detail to make definitive statements. The fear of this condition has driven many of the current return-to-play guidelines following concussion. Diffuse cerebral swelling (DCS) following a head injury is a well-recognized condition, more common in children than in adults, and usually has a poor outcome.