Repulsive guidance molecule A (RGMa) exhibits repulsive guidance of axonal growth and regulates neuronal differentiation during development of the mammalian brain. In this commentary, we describe the findings of our recent paper, "Repulsive Guidance Molecule A Suppresses Adult Neurogenesis," and discuss a possible model for RGMa suppression of newborn neurons that fail to properly migrate into the granular cell layer. In the study, we provided evidence that RGMa suppressed neurite growth and survival of newborn neurons in the adult dentate gyrus. This effect depends on the multifunctional Neogenin receptor expressed in adult neural stem cells through activation of the Rho-associated protein kinase leading to neurite growth inhibition and ultimately cell death. It should be noted that both RGMa and Neogenin interact with several well-described molecules, including bone morphogenetic proteins, that regulate neuronal development. Thus, it is likely that RGMa interacts with other intricate molecular networks that regulate adult neurogenesis.