A prospective study was carried out on ski accidents caused by collisions on ski slopes. The article defines the term "ski collision" and then reviews the authors' case histories of the last three years, taking the location and time of accident, the type of collision and injury into consideration. The authors have been able to prove that the collision type of injury differs from "normal" ski injury. The most striking difference in these injuries was found to be the increase in the frequency of visceral cranium trauma. The second difference concerns the incidence of thoracoabdominal injuries. The authors have attempted to point out a few prophylactic measures. A brief discussion deals with problems involving "slope regulations". Finally, the authors urgently recommend, in view of the risk of fatal injuries in collision accidents, to ensure quickest possible and careful transportation of accident victims to a versatile and well-equipped hospital.