During the last decade it has been definitively established that the genesis of new neurons can occur in the central nervous system of adult mammals, starting from neural stem cell compartments localized at specific sites. Although the anatomical and functional aspects of these processes have been deeply addressed in rodents (rat and mouse), recent findings do suggest that important differences do exist if comparing different mammalian species, including primates and humans. Striking differences have been described even in species closely related to laboratory rodents, such as the rabbit. They involve a different organization of the neurogenetic sites as well as possible different destinations and mode of cell migration of the progeny. These results are reviewed and discussed in the perspective of understanding the rules allowing adult neurogenesis to occur in the nervous system of different mammals.