The purpose of this study was to develop and cross-validate a generalized equation for predicting VO2peak from 1-mile run/walk (MRW) time and demographic variables in youth and young adults. Data for 753 males and females 8-25 yr of age were divided into validation (N = 495) and cross-validation (N = 258) samples. The validation sample was used to develop a multiple regression equation for predicting treadmill VO2peak (ml.kg-1.min-1) from gender (0 = F, 1 = M), age (yr), body mass index (kg.m-2; BMI) and MRW time (min). The multiple correlation (R) and standard error of estimate (SEE) were: R = 0.71, SEE = 4.8 ml.kg-1.min-1. The accuracy of this equation was confirmed when applied to the cross-validation sample. The regression equation for the total sample was: VO2peak = -8.41 (MRW) + 0.34 (MRW)2 + 0.21 (Age x Gender) -0.84 (BMI) + 108.94, R = 0.72, SEE = 4.8 ml.kg-1.min-1. We conclude that the generalized equation provides valid estimates of VO2peak in youth and young adults. The equation should be useful for educators, clinicians, and researchers who would like to interpret results of the MRW test in terms of VO2peak.