The time course and specificity of the changes in dendritic morphology following deafferentation were examined in nucleus laminaris of young chickens. The dendrites of nucleus laminaris neurons are segregated into dorsal and ventral domains, which are innervated separately from the ipsilateral and contralateral nucleus magnocellularis, respectively. Transection of the crossed dorsal cochlear tract deafferents the ventral dendrites of nucleus laminaris bilaterally without interrupting the matching input to the dorsal dendrites. In 10-day-old chicks, atrophy of the ventral dendrites began immediately after transecting the tract; the ventral dendrites were 10% shorter by 1 hour and 16% shorter by 2 hours after deafferentation. The length of the ventral dendrites progressively decreased over the next 2 weeks, resulting in at least a 60% loss of ventral dendrite 16 days after surgery. The dorsal dendrites of the same cells, whose afferents remained intact, did not change in length during the time course of this study. However, 16 days after the lesion, spines appeared on the normally smooth dorsal and ventral dendrites. The time course of dendritic atrophy and its restriction to the deafferented postsynaptic surface are related to possible mechanisms by which afferents regulate and maintain their target neurons.