Following horseradish peroxidase (HRP) injections in the superior, in the Deiters', in the medial, and in the descending vestibular nuclei in the hen, labeled cells are found in lateral longitudinal zones in the ipsilateral cerebellar cortex, most numerously in the anterior lobe, the nodulus, the uvula, and the auricle. Furthermore, labeled cells are found bilaterally in the ventral parts of the medial and intermediate cerebellar nuclei. Lesions in the cerebellar cortex of the anterior lobe and in anterior parts of the posterior lobe result in terminal degeneration, mainly in the nucleus Deiters dorsalis, but also scantily, in peripheral regions of the superior nucleus, the nucleus Deiters ventralis, the ventrolateral part of the medial nucleus and, mainly medially, in the descending nucleus. Lesions in the posterior part of the uvula, in the nodulus, and in the auricle result in much denser degeneration, most heavily affecting the nucleus Deiters dorsalis, but also affecting peripheral regions of the superior nucleus, the nucleus Deiters ventralis, the entire descending and medial nuclei, and the tangential nucleus. Lesions in the medial cerebellar nucleus result in degeneration bilaterally in the vestibular complex, most heavily affecting the nucleus Deiters ventralis and cell group B, but also affecting peripheral regions of the superior nucleus, the medial nucleus- mainly in dorsomedial regions, lateral and caudal parts of the descending nucleus and, very scantily, in the nucleus Deiters dorsalis. The findings are discussed in the light of the data concerning the organization of the cerebellovestibular projections in mammals and the known connections of the vestibular nuclei in birds.