Primary cilia are cellular appendages that provide important sensory functions and defects in primary ciliary signaling have been implicated in the pathophysiology of human diseases and developmental abnormalities. Almost all human cell types possess a primary cilium. Neurons throughout the brain possess primary cilia on which certain receptors localize, suggesting that neurons possess cilia-mediated signaling. However, the functional significance of neuronal cilia is unknown. Although there is a great deal of interest in understanding the functions of neuronal cilia, their study is hampered by the lack of an in vitro model system. We report that the majority of hippocampal neurons cultured from postnatal mice possess primary cilia in vitro. Further, we describe cilia proteins that can be labeled to readily visualize neuronal primary cilia in culture. These findings are the first characterization of neuronal primary cilia in vitro and should greatly facilitate further investigations into the function of these organelles. © 2007 Wiley-Liss, Inc.