Purpose: The purpose of this study was to evaluate the use of a treadmill walk-jog-run exercise test previously validated in adults and physical activity questionnaire data to estimate maximum oxygen consumption (VO[subscript 2]max) in boys (n = 62) and girls (n = 66) aged 12 to 17 years old. Methods: Data were collected from Physical Activity Rating (PA-R) and Perceived Functional Ability (PFA) questionnaires, a walk-jog-run submaximal treadmill exercise test, and a maximal graded exercise test. Results: Regression analysis resulted in the development of 2 models to predict VO[subscript 2]max. Submaximal exercise test data were used to build the following model (R[superscript 2] = 0.73; SEE = 4.59 mL [times] kg[superscript -1] [times] min[superscript -1]): VO[subscript 2]max (mL [times] kg[superscript -1] [times] min[superscript -1]) = 26.890 + (5.877 × Gender; 0 = female; 1 = male) - (0.782 × Body Mass Index [BMI])+(0.438 × PFA Score) + (2.712 × Treadmill Speed; mph) + (0.746 × Age) + (0.449 × PA-R Score). Maximal exercise test data were used to build the following model (R[superscript 2] = 0.83; SEE = 3.63 mL [times] kg[superscript -1] [times] min[superscript -1]): VO[subscript 2]max (mL [times] kg[superscript -1] [times] min[superscript -1]) = 10.716 + (1.334 × Maximal Treadmill Grade) + (5.203 × Treadmill Speed; mph) + (3.494 × Gender; 0 = female; 1 = male) - (0.413 × BMI) + (0.249 × PFA). Conclusions: The results of this study demonstrate, for the first time, that regression equations that use both exercise data and physical activity questionnaire data can accurately predict VO[subscript 2]max in youth. The submaximal and maximal exercise tests that use self-selected treadmill speeds can be used to assess cardiorespiratory fitness of youth with a wide range of fitness levels.