Olivocerebellar fibers from different subnuclei of the rostral inferior olive decussate in the brain stem and terminate as climbing fibers in one or two narrow, longitudinally arranged zones of the cerebellar cortex. These fibers issue collaterals to the central cerebellar nucleus that receives its afferents from the same cortical zone in which the parent fibers terminate. The rostral medial accessory olive projects to zone C2 and sends collaterals to the posterior interposed nucleus. A differentiation can be made between the rostral pole of this subnucleus which projects primarily to the paraflocculus and the ansiform lobule. More caudal areas connect with zone C2 in the anterior lobe and the paramedian lobule. The dorsomedial cell column projects to a lateral zone (zone A2) of lobule IX and more rostrolateral portions of the medial accessory olive supply a still more lateral zone of this lobule. The rostral half of the dorsal accessory olive sends fibers to zones C1 and C3. These fibers issue collaterals to the anterior interposed nucleus. A distinction can be made between the ventrolateral dorsal accessory olive, projecting to lobules II-IV and the ventral folia of the paramedian lobule and the dorsomedial portion of the rostral dorsal accessory olive that connects with lobules V, VI and the dorsal folia of the paramedian lobule. The most rostral part of the dorsal accessory olive provides more fibers into zone C3, more caudally located cells distribute primarily to zone C1. The rostral principal olive is connected with zone D and collateral terminations are found in the lateral cerebellar nucleus. In the paraflocculus the D zone can be divided into subzones D1 and D2. This study further substantiates the similarity in the organization of corticonuclear and olivocerebellar connections. The results are in general agreement with other recent investigations on the olivocerebellar system (Armstrong et al., '74; Brodal et al., '75; Brodal, '76; Hoddevik et al., '76; Brodal and Walberg, '77a,b; Oscarsson, '73, '76; Oscarsson and Sjölund, '77a,b).