Initial studies on neural stem cell biology were performed mainly with embryonic stem cells, but exciting discoveries and advances in knowledge about tissue-specific stem cells have emerged in the last few years. This review focuses on stem and/or progenitor cells in the brain that drive adult neurogenesis in mammals. Neuronal precursor cells are found in two regions of the adult brain: the subventricular zone and the hippocampus. Adult neurogenesis in the subventricular zone has implications for behavior and olfactory function and, in the hippocampus, is involved in mood, learning and memory. Several neurodegenerative diseases (e.g., Alzheimer's disease, Huntington's disease and Parkinson's disease) are increasing in frequency as the population is aging. Understanding the hormonal aspects of how adult neurogenesis is regulated could lead to advances in understanding, managing and eventually, treating neurodegenerative disorders. In this review, we summarize what is currently known about the influence of hormones on adult neurogenesis. Many hormones that act through nuclear receptors are implicated in regulating neural progenitor cell biology. Given that nuclear receptors are well defined, drugable targets, further research on their mechanisms of action in adult neurogenesis are likely to engender new replacement, repair and therapeutic approaches.