Abstract Background Recent research has shown that the Fitkids Treadmill Test (FTT) is a valid and reproducible exercise test for the assessment of aerobic exercise capacity in children and adolescents who are healthy. Objective The study objective was to provide sex- and age-related normative values for FTT performance in children and adolescents who were healthy, developing typically, and 6 to 18 years of age. Design This was a cross-sectional, observational study. Methods Three hundred fifty-six children and adolescents who were healthy (174 boys and 182 girls; mean age=12.9 years, SD=3.7) performed the FTT to their maximal effort to assess time to exhaustion (TTE). The least-mean-square method was used to generate sex- and age-related centile charts (P3, P10, P25, P50, P75, P90, and P97) for TTE on the FTT. Results In boys, the reference curve (P50) showed an almost linear increase in TTE with age, from 8.8 minutes at 6 years of age to 16.1 minutes at 18 years of age. In girls, the P50 values for TTE increased from 8.8 minutes at 6 years of age to 12.5 minutes at 18 years of age, with a plateau in TTE starting at approximately 10 years of age. Limitations Youth who were not white were underrepresented in this study. Conclusions This study describes sex- and age-related normative values for FTT performance in children and adolescents who were healthy, developing typically, and 6 to 18 years of age. These age- and sex-related normative values will increase the usefulness of the FTT in clinical practice.