This fact sheet uses a question-and-answer format to summarize what is known about preventing mental retardation through use of bicycle helmets. Questions and answers address the following topics: the importance of bicycle helmets; the number of bike riders injured or killed each year in bicycle crashes (about 1,000 killed, over 500,000 people injured, of whom 32.5 percent suffer head injuries); data on children and bicycle head injuries (138,000 per year); the rate of helmet usage for bicycle riders (fewer than 2 percent of children), despite the evidence that helmet usage reduces head injuries by 85 percent; tips for choosing and fitting a bicycle helmet; barriers to children's helmet use (lack of awareness of the need, cost, and peer pressure); and what states and communities are doing and can do to increase use of bicycle helmets. Additional organizational and print resources are listed. (DB)