NeuroD/BETA2, a basic helix-loop-helix transcription factor, has been shown to play a role in tissue-specific differentiation of pancreatic and enteroendocrine cells. To gain further insight into the function of neuroD/BETA2 in the nervous system development, we examined the expression pattern of neuroD/BETA2 during embryonic and postnatal development by using in situ hybridization. Dynamic changes of neuroD/BETA2 expression in the central nervous system were observed during embryogenesis, especially in telencephalon, hippocampus, cerebellum, spinal cord, and olfactory epithelium. Moderate level of expression was also detected in developing pancreas in early embryogenesis. Although the neuroD/BETA2 expression in cerebellum and hippocampus increased over time, expression in cerebral cortex, spinal cord, as well as in fetal pancreas gradually decreased as embryogenesis proceeded. High level of the neuroD/BETA2 expression in developing cerebellum and hippocampus persisted throughout postnatal development and remained at a stable level in the adult brain. Interestingly, neuroD/BETA2 expression was detected not only in postmitotic but also in mitotic cells, as was evident in its expression in external granular layer of cerebellum and granule cells of the dentate gyrus during postnatal development. This observation suggests that neuroD/BETA2 may have a unique role in proliferation, differentiation, or both, of granule cells of cerebellum and dentate gyrus.