We examined the effect of a neonatal sensorineural hearing loss on the soma area of neurones in the central nucleus of the inferior colliculus (ICC) in adult cats to evaluate the role of auditory experience on neuronal atrophy within the auditory midbrain. Three groups of animals were used: bilaterally deafened, unilaterally deafened and normal hearing controls. Soma area measurements were made from the laminated central and medial divisions of the ICC of eight deafened and two normal hearing cats. A small but significant reduction in soma area was evident for bilaterally deafened animals compared with normal hearing controls (P<0.05, Dunnett's test). In contrast, there was no significant difference in mean soma area between normal hearing and unilaterally deafened animals (P0.05) irrespective of whether the ICC examined was ipsi- or contralateral to the deafened ear. These results demonstrate that the reduction in soma area of auditory brainstem neurones reported following a sensorineural hearing loss is also evident at the level of the auditory midbrain.