The multi-stage 20-m shuttle run test (MSRT) is one of the most popular field tests using equations based on test results or the final speed for an indirect estimation of maximal oxygen uptake (VO2max). The aim of this study was to compare the real VO2max value to the predicted value of VO2max by MSRT and rate the usefulness of the MSRT as a predictor of VO2max in young football players. Fifteen young football players, nominees for the 2004/2005 national Under-18 team, were included in this study. The subjects were 17.9 +/-.2 years old, had an average height of 178.8 +/- 7 cm and an average weight of 71.8 +/- 7.5 kg. The players came from different Slovenian junior premier football league clubs and trained on average 4 to 5 times per week. Testing was conducted on all subjects over two days, between 9 a.m. and 2 p.m., on synthetic turf. A mobile device for the measurement of O-2 and CO2 in expired air and ventilation during MSRT was used. On the basis of the test result (the number of levels and repetitions between them) VO2max was calculated. The correlation between the measured and predicted VO2max was determined with Pearson's correlation coefficient. The comparison of both mean values showed that the measured value was significantly higher (p<.05), by as much as 8.5 ml O-2 kg(-1).min(-1), than the MSRT-predicted VO2max. Variables were statistically correlated, but the correlation coefficient amounted to only .58. This study has shown that an indirect evaluation of aerobic capacity based on the multi-stage 20 m shuttle run test can lead to wrong conclusions in young soccer players. The correlation observed between the measured and predicted VO2max was too weak to predict the aerobic capacity of young football players with certainty.