Peak oxygen uptake (V'O(2)peak) is recognised as the best expression of aerobic fitness. Therefore, it is essential that V'O(2)peak reference values are accurate for interpreting a cardiopulmonary exercise test (CPET). These values are country specific and influenced by underlying biological ageing processes. They are normally stratified per paediatric and adult population, resulting in a discontinuity at the transition point between prediction equations. There are currently no age-related reference values available for the lifespan of individuals in the Dutch population. The aim of this study is to determine the best-fitting regression model for V'O(2)peak in the healthy Dutch paediatric and adult populations in relation to age. In this retrospective study, CPET cycle ergometry results of 4477 subjects without reported somatic diseases were included (907 females, age 7.9-65.0 years). Generalised additive models were employed to determine the best-fitting regression model. Cross-validation was performed against an independent dataset consisting of 3518 subjects (170 females, age 6.8-59.0 years). An additive model was the best fitting with the largest predictive accuracy in both the primary (adjusted R-2=0.57, standard error of the estimate (SEE)=556.50 mL.min(-1)) and cross-validation (adjusted R-2=0.57, SEE=473.15 mL.min(-1)) dataset. This study provides a robust additive regression model for V'O(2)peak in the Dutch population.