Body composition of 1815 North-Italian young sports participants in relation to sex, age, sport and level of performance was investigated. About thickness and anatomical distribution of subcutaneous fat females showed skinfolds thicker than males. Significant differences were observed in skinfold thicknesses means of different sport-groups. Subscapular and forearm skinfolds were the best discriminant variables for males and females respectively. Body density was estimated according to Katch and McArdle (1973) and Durnin and Womersley (1974) equations. Males showed higher body density and lower fat percentage values than females. The lowest value of body density and the highest fat percentage were in male martial art competitors and in females practising skating and athletics. The highest values of body density and the lowest of fat percentage were in males practising athletics and rowing and in female martial art competitors. Highest and lowest values of fat-free mass were in games players and in soccer players and gymnasts respectively. "High aptitude" subjects showed higher fat-free mass values than "middle aptitude" group, besides a tendency towards higher body density values and lower fat percentage than "middle aptitude" group. With aging body density decreased whereas fat percentage and fat-free mass increased.