The objective was to estimate the contribution of experience, body size and maturity status to variation in the functional capacities of adolescent football (soccer) players. The sample included 69 players 13.2-15.1 years of age from three clubs which competed in the highest division for their age group in the first Portuguese national division. Height and weight were measured and stage of pubic hair development was assessed at clinical examination. The number of years of experience in football was obtained at interview. Three tests of functional capacity were administered: 30-m dash (running speed), vertical jump (explosive power) and a yo-yo intermittent endurance test (aerobic resistance). Multiple linear regression analysis was used to estimate the relative contributions of age, stage of sexual maturity, height, weight and years of formal training in football to the three indicators of functional capacity. Stage of puberty, body size and years of training accounted for 21% to 50% of the variance in the three tasks. Sexual maturity status was the primary contributor to the variance in the intermittent shuttle run, whereas weight and height were the primary contributors to the explained variance in the 30-m dash and vertical jump, respectively. In conclusion, biological maturity status significantly influences the functional capacity of adolescent football players 13-15 years of age. Training is a significant contributor to aerobic resistance, whereas weight and height are significant contributors to the sprint and vertical jump, respectively.