SUMMARY Data on hearing impairment are studied by using a three-parameter log-normal distribution, all of whose parameters depend on covariates. The fitting algorithm is an extension of generalized linear modelling. Questions for research include the estimation of a base-line distribution of hearing threshold levels for an 'unexposed' population and the development of a model that describes how the distribution changes with age and exposure to noise. The model gives a good description of data from a recent national survey.