The literature reports that many of the most serious ski injuries, such as those resulting from a collision with another skier or with a fixed object, occur after skiers have lost control. In this paper calculations are presented of skier trajectories, based on the skier's speed and direction at the moment of loss of control, and the simplifying assumptions of a constant coefficient of friction following the loss of control and a constant steepness of the slope during sliding. These relatively simple, ballistic calculations are used to approximate how far across and down a hill a skier can travel following loss of control, and under what conditions the skier will stop. The trajectories are referenced to the point where the skier's body contacts the snow, and the path of the skier is calculated across the snow surface. In addition, the distance traveled from the point of loss of control to where the skier's body contacts the snow is estimated, and the issue of whether to instruct skiers to fall after losing a ski (without falling) or to attempt to regain control on the remaining ski is discussed. The role that trajectory calculations could play in trail design and in the placement of protective devices is also discussed.