The projection of the vermis of the anterior and posterior lobes of the cerebellum to the fastigial nucleus was studied. It was attempted to obtain lesions restricted to the lobules and this was achieved for the posterior lobe only. The extent of lesions and of additional encroachments were determined by mapping degenerated descending cortical fibers in serial sections. Evidence was obtained that the projection of the vermis is restricted to the fastigial nucleus, without a contribution to the interposed nuclei, in the posterior lobe. Indirect evidence supports the existence of a similar arrangement in the anterior lobe. The projection appears to be distributed ipsilaterally. There is a topographical distribution of the cortical lobules in the different regions of the fastigial nucleus: each lobule projects to the nearest region of the nucleus. There is a divergence of the terminal ramifications of the axons originating from a given lobule within their area of termination. There is also an overlap between the borders of adjacent termination sites. It is concluded that there is a sequential representation of the cerebellar cortex in the fastigial nucleus.