Success in sports, as measured by competitive performance, is dependent upon a number of significant mental and physical components. Somatotype, motor skills, age, nutritional status, physiology, psychology, training level, genetic endowment, and injury risk are the major independent variables influencing performance. Unfortunately, the data available in this area of sports medicine are not always reliable or allow interstudy comparisons. This article reviews the historical and current information used to predict human performance in sports at the childhood and adolescent level. Although mesomorphy, and to a lesser extent ectomorphy, are positively associated with enhanced performance, successful athletes tend to have or acquire somatotypes characteristic of individuals already successful in a particular sport. For the most part, motor skills are age (chronological) and gender dependent. In general, the efficiency of movement progressively improves throughout childhood and into early adolescence and is highly dependent on environmental influences. A lower anaerobic and aerobic capacity reduces performance in the child and adolescent. Nonetheless, regular training can favourably improve motor skills and physiological fitness parameters. The relationship between endurance performance and aerobic capacity, however, is not strong at any age during childhood. Performance levels are reduced if nutrition is inadequate. A number of mental factors such as aggression, spirit, and self-confidence are also related to sports performance, although their correlation is unclear at present. Performance is influenced by the effect of genetic factors on specific traits in 30 to 85% of cases. Risk factors that negatively impact on performance levels include a history of previous injury, excessive training schedules, decreased fitness endurance, joint looseness or tightness, and certain personality traits. It is suggested that sport performance may be optimised by the early identification of individuals with positive genetic and somatotypic markers and negative risk factors. Motor skill development and physiological parameters can then be maximised by using regular, non-excessive training protocols, sound nutrition patterns, a safe environment and protective gear. Further investigations in this important area of sports medicine are essential in order to more fully characterise those criteria essential for successful sports participation. In particular, such studies should be purely longitudinal and should control for multiple confounding factors operating at different times.