Rationale: The NHANES III reference is currently recommended for interpreting spirometry results, but it is limited by the lack of subjects below 8 years of age and does not continuously model spirometry across all ages. Objectives: By collating pediatric data from other large population surveys, we have investigated ways of developing reference ranges that more accurately describe the relationship between spirometric lung function, height and age within the pediatric age range and allow a seamless transition to adulthood. Methods: Data were obtained from four surveys and included 3598 subjects aged 4-80 years. The original analyses were sex specific and limited to non-Hispanic Caucasian subjects. An extension of the LMS method, widely used to construct growth reference charts, was applied. Results: The extended models have three important advantages over the original NHANES III analysis in that they: 1) extend the reference data down to 4 years of age, 2) incorporate the relationship between height and age in a way that is biologically plausible 3) provide smoothly changing curves to describe the transition between childhood and adulthood, and 4) highlight the fact that the range of normal values is highly dependent on age. Conclusions: The modelling technique provides an elegant solution to a complex and longstanding problem. Furthermore it provides a biologically plausible and statistically robust means of developing continuous reference ranges from early childhood to old age. These dynamic models provide a platform from which future studies can be developed to continue to improve the accuracy of reference data for pulmonary function tests.