Published data on airway dimensions in the developing human lung, including estimated age-dependent changes and experimental data, have been summarized to illustrate the variability and gaps in the data used to develop anatomical models for deposition calculations. A comparison of the morphological dimensions resulting from various assumptions about the volume distribution of pulmonary airways is also presented. Although deposition is not examined here, the varibility in reported measurements underscores the influence that anatomical parameters can have on deposition calculations and the importance of further investigation of lung dimensions to reduce the uncertainties in computer simulations of delivered dose, thereby improving the data base necessary for risk assessment.