Factors affecting repeated sprint ability (RSA) were evaluated in a mixed-longitudinal sample of 48 elite basketball players 14 to 19 years of age (16.1±1.7 years). Players were observed on six occasions during the 2008-2009 and 2009-2010 seasons. Three basketball-specific field tests were administered on each occasion: the Shuttle Sprint Test (SST) for RSA, the Vertical Jump (VJ) for lower body explosive strength (power), and the Interval Shuttle Run Test (ISRT) for interval endurance capacity. Height and weight were measured; body composition was estimated (percent fat, lean body mass). Multilevel modeling of RSA development curve was used with 32 players (16.0±1.7 years) who had two or more observations. The 16 players (16.1±1.8 years) measured on only one occasion were used as a control group to evaluate the appropriateness of the model. Age, lower body explosive strength, and interval endurance capacity significantly contributed to RSA (p < .05). RSA improved with age from 14-17 years (p < .05) and reached a plateau at 17-19 years. Predicted RSA did not significantly differ from measured RSA in the control group (p > .05). The results suggest a potentially important role for the training of lower body explosive strength and interval endurance capacity in the development of RSA among youth basketball players. Age-specific reference values for RSA of youth players may assist basketball coaches in setting appropriate goals for individual players.