Swedish authorities have discussed making the use of helmets for snowmobile riders compulsory. To evaluate the possible injury-reducing potential of such a law, 245 non-fatally injured riders and 104 fatalities were analyzed. Non-minor (AIS > 1) head injuries were far less common than in motorcycling, and many fast driving young snowmobile riders seem to use helmets regardless of a law. The persons with head injuries who had not used helmets, or whose helmet use was unknown, had violated other laws, most often the Traffic Temperance Law, or the law forbidding driving on public roads. A helmet law for snowmobile riders will probably not increase the helmet use in this group and consequently have a negligible injury-reducing effect. Helmets are, however, strongly recommended, especially for riders who favour fast driving.