Neurodegenerative disorders and traumatic brain injury result in the loss of specific neuronal populations. Stem cells are self-renewing, multi- or pluripotent cells capable of differentiating into a wide range of cell types, properties which make stem cells a potentially invaluable source of transplantable cells. Recent experimental studies have indicated that several stem cell populations have the ability to replace lost neurons and to repair the damaged nervous system following transplantation. This review evaluates the potential of various stem cell populations in the treatment of human neurodegenerative conditions and traumatic brain injury.