The purpose of the study was to determine the hydration status, fluid intake and electrolyte losses of 21 male professional youth soccer players (age 17.1 ± 0.7 yr) training in a cool environment. Pre- and post training measurements of body mass, urine (freezing point osmolality method) and sweat concentration (flame emission spectroscopy) were collected. Fourteen players were found to be hypohydrated prior to training. The amount of fluid lost due to exercise equated to a 1.7 % loss in body mass, which equated to a gross dehydration loss of 0.5 %. Overall, the soccer players replaced 46 ¬± 88% of sweat loss during training and only four remained hypohydrated after training. No significant correlations between sweat loss and sweat concentrations of Na+ (r = -0.11, P = 0.67), K+ (r = 0.14, P = 0.58) were found, but there was a significant correlation with Mg2+ (r = -0.58, P < 0.009). This study found large variability in pre-training hydrationstatus which the players were able to rehydrate during the training sessions.However, given the numbers starting training in a hypohydrated state, adequate hydration status prior to training should be considered by youth players, coaches and sports science support staff.