The use of dieting, rapid weight loss, and frequent weight fluctuation among athletes competing in weight-class and leanness sports have been considered a problem for years, but the extent of the problem and the health and performance consequences have yet to be fully examined. Most studies examining these issues have had weak methodology. However, results from this review indicate that a high proportion of athletes are using extreme weight-control methods and that the rules of some sports might be associated with the risk of continuous dieting, energy deficit, and/or use of extreme weight-loss methods that can be detrimental to health and performance. Thus, preventive strategies are justified for medical as well as performance reasons. The most urgent needs are: (1) to develop sport-specific educational programmes for athletic trainers, coaches, and athletes; (2) modifications to regulations; and (3) research related to minimum percentage body fat and judging patterns.