We assessed the criterion related validity of 1/2 mile run/walk (1/2MRW) test for estimating VO2peak in children aged 6-17 years. The criterion related validity of the Fernhall's equation in a sub-group of children aged 10-17 years was also examined. A total of 86 children completed a maximal graded treadmill test and the 1/2MRW test. The cohort was randomly divided into either validation (n=47) or a cross-validation (n=39) group. A regression equation was computed and assessed through several error measures, and the Bland and Altman method. There was no systematic bias in the validation group nor in the cross-validation group (P > 0.1). The root mean sum of squared errors (RMSE), and the percentage error were 6.5 ml/kg/min, and 13.9%, respectively. These figures were very similar in the cross-validation group. The new equation had a lower RMSE and percentage error than the Fernhall's Equation (6.2 vs. 19.7 ml/kg/min, and 16% vs. 50.4%, respectively, P<0.001). The Fernhall's equation showed a significant underestimation of VO2peak (18.1 ml/kg/min, P<0.001). In conclusion, the new regression equation is valid for estimating VO2peak from the 1/2MRW time, sex, and body mass index in healthy children aged 6-17 years, and is more accurate than Fernhall's equation in the sample studied.