The shapes of the apical and basal dendritic fields of the fusiform cells in the dorsal cochlear nucleus of the hamster were analyzed quantitatively. Measurements of the cross-sectional areas of the dendritic fields in planes parallel and perpendicular to planes occupied by the cochlear nerve axons revealed that the apical dendrites have a preferential orientation with respect to the cochlear planes. No consistent orientation of the basal dendrites was apparent. The orientation of the apical dendrites is not present in the neonatal hamster; rather, it develops gradually and is not fully established until after postnatal day 25. Since the cochlear fibers grow into the dorsal cochlear nucleus, establish contacts and become functional before day 25, the presence of the cochlear input might be a prerequisite for the development of oriented dendritic trees. In adult hamsters that have had their cochlear input eliminated during infancy, the apical dendritic trees of the fusiform cells are not oriented normally. The results suggest that the presence of the afferent input is necessary for the differential growth that leads to the development of oriented dendritic trees.