Recent evidence suggests that nitric oxide (NO) has a remarkable anti-proliferative action towards dividing neural precursor cells as well as towards cells giving rise to neural-derived tumors. The present paper summarizes essential literature-derived information on this issue and provides novel experimental evidence for these NO-mediated actions regarding a well characterized population of neuronal precursors, the cerebellar granule cell precursors and a cell line of medulloblastoma, a pediatric tumor originating from these same precursor cells undergoing deregulated proliferation. Evidence is presented regarding the NO-mediated regulation of proliferation of neuronal precursor cells both during developmental and adult neurogenesis. Then, the role of NO in the control of proliferation of neural-derived tumor cells, such as PC12 and neuroblastoma cells, is discussed. Novel experimental data are provided documenting the anti-proliferative action of NO towards basal and mitogen-stimulated division of rat cerebellar granule cell precursors, as well as towards medulloblastoma DAOY cells. Finally, some molecular correlates of NO action on cell cycle regulation are discussed. Overall, the data presented and discussed here highlight similarities at the molecular level between physiologic processes regulating normal proliferation of neural precursors and pathologic deregulation of these processes leading to tumor formation.