OBJECTIVE Post-exercise cardiac troponin T (cTnT) release has been widely reported in adult athletes but limited data is available for adolescents. The aim of this study was to determine the incidence and magnitude of cTnT appearance in a large group of adolescent runners, and to determine any association between cTnT release and personal characteristics of adolescents. METHODS We recruited 63 adolescent runners (mean±SD: age 16.4±1.5 years; 10 females) who all completed a simulated half-marathon race (an all-out 21-km run) during routine training. Personal data collected included age, training history, 21-km run performance as well as pre-post exercise serum cTnT levels. Serum cTnT was assayed using a 3rd generation assay. RESULTS At pre-exercise, cTnT concentrations were below the 0.01 µg/L cTnT detection limit of assay in 58/63 runners. The post-exercise cTnT level (range: <0.01-1.36 µg/L) was significantly (p<0.001) greater than that of the pre-exercise (range: <0.01-0.02 µg/L). After the exercise, 57 (90%) and 44 (70%) subjects had cTnT concentrations above the detection: 0.01, and clinical thresholds: 0.05 µg/L, respectively. Post-exercise cTnT was inversely correlated with training years (r=-0.25, p<0.05) and age (r=-0.31, p<0.05). Compared with runners who had trained for ≥ 3 years, runners with less training experience demonstrated increased post-race cTnT levels (p<0.01). CONCLUSIONS cTnT increases are virtually universal among adolescent runners following a 21-km run during routine training and can reach levels typically diagnostic for acute myocardial infarction potentially initiating diagnostic dilemmas. Adolescents with less training experience had higher post-exercise cTnT.