The neural system controlling song in birds has proven a useful model for investigating how neuronal growth and survival are regulated by sexual differentiation. The present study focused on one song control area, the robust nucleus of the archistriatum (RA), and explored how sex differences in the proliferation of putative glia cells in this region influence sexually dimorphic cell survival. In zebra finches (Poephila guttata), RA neuron death is much greater in young females than in males, resulting in marked sex differences in RA neuron number. An earlier study indicated that just prior to this sexually dimorphic neuron death the proliferation of putative glia cells within the RA is significantly lower in females than in males and remains so throughout the peak of neuron death. This suggests that sex differences in glia (or glia-derived molecules) might regulate neuron survival during sexual differentiation of the RA. To determine whether increased cell proliferation within the RA favors increased cell survival, we infused the potent glia mitogen fibroblast growth factor-2 (FGF-2) into the RA unilaterally in young females. We find that FGF-2 infusions increase RA cell proliferation and concurrently decrease the incidence of degenerating RA cells, results consistent with the hypothesis that glia exert neurotrophic effects on RA neurons during sexual differentiation.