The Smoothened (Smo) receptor is a key transducer of the Sonic Hedgehog (Shh) signaling pathway in the brain. Recent studies in rodents have highlighted its major role in the maintenance of neural stem and progenitor cells in the two main neurogenic niches of the adult brain: the subventricular zone of the lateral ventricles and the subgranular zone of the dentate gyrus in the hippocampus. Smo may also regulate brain responses to various injuries, and its modulation in the primary cilia of brain cells is essential for regulating Shh signals. Recent clinical trials have underlined the therapeutic value of some Smo antagonists for the treatment of Hedgehog-linked medulloblastomas. Here, we review recent findings on the roles of Smo in the adult brain, and unravel research on the clinical implications for the treatment of brain diseases, that are increasingly under investigation.