The olfactostriatum is a portion of the basal ganglia of snakes situated ventromedially to the nucleus accumbens proper. It receives a major vomeronasal input from the nucleus sphericus, the primary target of accessory olfactory bulb efferents. Recently, the ophidian olfactostriatum has been characterized on the basis of chemoarchitecture (distribution of serotonin, neuropeptide Y and tyrosine hydroxylase) and hodology (afferent and efferent connections). In contrast to the nucleus accumbens proper, the olfactostriatum is densely immunoreactive for serotonin and neuropeptide Y and sparsely immunoreactive for tyrosine hydroxylase. The nucleus accumbens proper and the olfactostriatum share most afferent connections except those originating in the nucleus sphericus, which are exclusively directed to the olfactostriatum. Similarly, the nucleus accumbens proper and the olfactostriatum show a similar pattern of efferent connections including those going to the ventral pallidum, although the olfactostriatum alone projects to the main and accessory olfactory bulbs as well as some amygdaloid nuclei. On the basis of its chemoarchitecture, the olfactostriatum resembles the mammalian ventral pallidum (but also the shell of the nucleus accumbens). Its connections, however, suggests that the olfactostriatum could be a specialized portion of the shell of nucleus accumbens extended more ventromedially than previously believed and devoted to processing vomeronasal information. Comparative data suggest that a similar structure is present in the basal ganglia of amphibians and mammals.