After restricted cochlear lesions in adult animals, the frequency selectivity of neurons in the cortical region deprived of its normal input by the lesion is changed such that the region is occupied by expanded representations of adjacent (perilesion) frequencies. Analogous changes in cortical frequency selectivity and organization are seen as a consequence of behavioral training that enhances the significance of particular acoustic stimuli. The occurrence of such reorganization in a wide range of species (including simian primates) suggests that it would also occur in humans. Direct evidence in support of this suggestion is provided by a small body of functional imaging evidence. Although such reorganization almost certainly does not have a compensatory function, such a profound change in the pattern of cortical activation produced by stimuli exciting perilesion parts of the receptor epithelium would be expected to have perceptual consequences and, perhaps, clinical implications.