Whizzing down a snow-covered hill may be exhilarating, but roughly 33,000 people a year are treated in emergency rooms for sledding-related injuries. Collisions are typically the cause, reports the nonprofit National Safety Council. Fractures, cuts, and bruises are the most common injuries, though more serious damage is possible. "I've seen bleeds, organ injuries, and even some fatalities," says Ryan Stanton, an emergency-room physician in Lexington, Ky. "A sled doesn't provide you with any protection, so when that plastic hits a tree, a fence, or a pole, the acceleration carries you into it." That's why it's smart to wear a bicycle helmet while sledding (or skiing, snow tubing, or snowboarding). Avoid rocky hills and areas dotted with trees, fences, utility poles, or other obstacles. Never sled head-first, and sit up instead of lying on your back. And if the sled begins flying out of control, roll off, Stanton says.