Thymosin beta 4 (Tβ4), a small acidic peptide isolated originally from calf thymus, is recognized as a regulator of actin polymerization. It is widely distributed in the brain, in neurons as well as in microglia, and it has been implicated in lesion-induced neuroplasticity. In the present study, we quantitatively analyzed the immunocytochemical expression pattern of Tβ4 in the superior colliculus (SC) of the adult mouse following monocular enucleation. Immunocytochemistry revealed a remarkable neuronal profile in the SC of 2, 5 and 7-week enucleated animals. We investigated the morphology, number and layer-specific localization of these immunoreactive neurons. Neuronal Tβ4-immunoreactive cell bodies were only sparsely found in the deep layers of the SC of control mice and showed only few and short immunoreactive branches, whereas their number increased significantly with post-enucleation survival time, as well as the total extent of the neuritic tree and its degree of branching. Occasionally, some Tβ4-immunoreactive neurons were also detected in the periaqueductal gray. As a regulator of actin metabolism, Tβ4 may influence the remodeling of these collicular neuronal processes, possibly in the context of a re-alignment of the sensory and motor maps in the deep SC as a consequence of the visual deprivation paradigm.