The International Commission on Radiological Protection has recently endorsed a new model of the human respiratory tract. This model has been used to calculate the effective dose per unit exposure to radon progeny in mines or homes. The resulting effective dose per unit exposure is between 2 and 3 times that suggested by epidemiological approaches: dosimetry estimates are around 15 mSv per WLM, while epidemiological estimates are around 5 mSv per WLM. In an attempt to reconcile these two estimates, a detailed examination of the underlying assumptions made in the dosimetric approach has been performed. The sources of uncertainty in the final estimate of effective dose per unit exposure to radon progeny, E/P(p), have been divided into uncertainty in (a) aerosol conditions, (b) ICRP respiratory tract model parameters, and (c) other ICRP assumptions used in the calculation. Furthermore, the uncertainty of E/P(p) to parameters which ICRP had not intended the user of the model to adjust, (d) the cell depths, thicknesses, and sensitivities of the target cell layers themselves, has been investigated. A sensitivity analysis of E/P(p) to parameters in each of these categories has been performed. Probability distributions of all the parameters that affect E/P(p) have been generated, and in order to propagate these uncertainties, a Monte Carlo type simulation based on the Latin Hypercube sampling method has been performed. The conclusion is that the dosimetry based estimate of E/P(p) is unlikely to be reconciled with the epidemiological estimate of 5 mSv per WLM unless at least one of the values of the risk-weighting factors, currently recommended by ICRP, is reconsidered.