The purpose of this study was to compare symptoms of exercise-induced muscle damage following an initial and repeated bout of plyometric exercise in men and boys. Ten boys (9-10 y) and ten men (20-29 y) completed two bouts of eight sets of ten plyometric jumps, two weeks apart. Perceived soreness (0-10, VAS), isometric strength (STR) of the quadriceps at six knee flexion angles, counter-movement jump (CMJ) and squat jump (SJ) height were assessed before and at 30 min, 24 h, 48 h and 72 h after each bout. All variables followed the expected patterns of change in men, with soreness peaking at 24 - 48 h (5.8 ± 1.7) and decrements in muscle function peaking at 30 min after the first bout (73 - 85 % of baseline scores). Symptoms remained for 72 h after the first bout in men. In boys, symptoms were much less severe and peaked at 30 min (VAS = 2.1 ± 1.8, functional decrements 87 - 92% of baseline) and, with the exception of soreness, returned to baseline after 24 h. After the second bout of plyometric exercise, the level of soreness and decrements in CMJ, SJ and STR were lower, although the effect was stronger in men, in all cases. The results of this study suggest that whilst children may experience symptoms of muscle damage after intensive plyometric exercise, they are much less severe. A prior bout of plyometric exercise also appears to provide children with some protection from soreness following a subsequent bout of plyometric exercise. Explanations for milder symptoms of exercise-induced muscle damage in children include: greater flexibility leading to less over-extension of sarcomeres during eccentric exercise, fewer fast-twitch muscle fibres and greater and perhaps more varied habitual physical activity patterns.