The physical activity required for most sports has numerous health benefitsVphysical, mental, and academic (5,22,35). Some young athletes specialize in a single sport, while others play multiple sports throughout adolescence. Primary reasons to specialize early include enjoying that single sport; lifestyle access to a particular sport, such as running (34); hope for financial or other special success; or parental pressure. Regions with few resources expect organized sports may provide a safer environment for physical activity than the outdoor neighborhood (e.g., South Africa and Brazil) or increase government-supplied resources to youth sports organizations based on the number of children enrolled (Australia (1)). Recent concerns by sports medicine experts have sparked debate about the wisdom of early sports specialization (3Y6,21,36), but virtually no solid data have been published to inform caregivers, coaches, and families about possible risks and benefits. Sports specialization below the age of 18 yr has been suggested to increase injury risk, decrease social opportunity, and impair life satisfaction (4,16). Additional review articles (23,24) and consensus statements by major sports medicine organizations (3Y5,8,21,36) suggest that early specialization is a culprit potentially leading to adults with history of excessive injuries and limited social opportunity, even suggesting dire consequences (24). However, research supporting these statements is minimal or absent.