In this study, we identified neuronal precursors that can disperse through adult mammalian brain tissue. Transplanted neuronal precursors from embryonic medial ganglionic eminence (MGE), but not from lateral ganglionic eminence (LGE) or neocortex, dispersed and differentiated into neurons in multiple adult brain regions. In contrast, only LGE cells were able to migrate efficiently from the adult subventricular zone to the olfactory bulb. In embryonic brain slices, MGE cells migrated extensively toward cortex. Our results demonstrate that cells in different germinal regions have unique migratory potentials, and that adult mammalian brain can support widespread dispersion of specific populations of neuronal precursors. These findings could be useful in repair of diffuse brain damage.