Neurogenesis occurs in the adult brain and neural stem cells (NSCs) reside in the adult central nervous system (CNS) of mammals. Adult NSCs offer tremendous potential for cellular therapy for the treatment of neurological diseases and injuries, particularly of Alzheimer's disease (AD). The contribution of newly generated neuronal cells of the adult brain to the functioning of the nervous system remains to be elucidated. Neurogenesis is enhanced in the brain of patients with AD. Enhanced neurogenesis would contribute to regenerative attempts in AD, to compensate for the neuronal loss. Adult neurogenesis holds the potential to generate aneuploid cells, a landmark of AD pathology. Aneuploid newly generated neuronal cells in the adult brain would contribute to the pathogenesis of AD. Adult neurogenesis would not only be beneficial, but also detrimental for patients with AD. We will review and discuss the potential of adult NSCs for the treatment of AD and their contribution to the pathogenesis of the disease, as well as the development of novel drugs and therapies for treating AD.