The number of potentially intimate relationships between brain tumors and the precursor cells that contribute to normal central nervous system (CNS) development and repair now appears to be somewhat larger than would have been anticipated only a few years ago. It also appears that understanding the vulnerabilities of CNS precursor cells, and of the specific cells that they generate, might help us to reveal the biological basis for the cognitive impairment that is increasingly recognized as an adverse effect of systemic cancer therapies. Using neural stem cells as therapeutic vehicles in the treatment of brain tumors could be modified to allow repair of the damage caused by brain tumors themselves and of the neurological impairment that is frequently associated with traditional cancer treatment approaches.