The health benefits associated with youth sports participation are well recognized. At the elite level, however, are these advantages in fact outweighed by an increased risk of injury and illness? There are strong opinions in the public debate on how to best achieve success in youth sport, but research is limited. Specialized sport academy high-schools enable youth athletes to combine a college-entry high school program with sports at the elite level. There is no consensus, however, on when intensive, sport-specific training programs need to start, what the requirements are for youth elite athletes to improve skills vs. minimizing injury and illness risk, and how physical and mental overload can best be avoided. The purpose of this thesis was to increase the level of knowledge about the magnitude of health problems in youth elite athletes as well as to examine potential associations between injury and illness and early single-sport specialization, performance level, and physical fitness level. Nearly half of the youth elite athletes (43%) attending specialized sport academy high schools reported a health problem every week, and 25% reported a substantial health problem weekly. Girls reported more health problems than boys (53% vs. 39%). More injuries were reported in team sports (37%) and technical sports (36%), whereas more illnesses were reported among the endurance athletes (23%). Team sport athletes reported more substantial injuries than their teammates. In our study, neither early specialization nor single-sport specialization appeared to represent risk factors for injury and illness among the youth elite athletes after enrollment into a specialized sport academy high-school environment. Similarly, neither high performance level nor low physical-fitness level appeared to represent risk factors for injury and illness among the youth elite athletes. The large burden of health problems applied to these youth athletes, however, is a concern, and further preventative work is warranted.