Background: BAI1 is an adhesion receptor; little is known about its signaling or localization. Results: BAI1 activates Rho in a G protein-dependent manner, binds to synaptic scaffold proteins, and is highly enriched in the postsynaptic density. Conclusion: BAI1 is a synaptic receptor that signals through G proteins. Significance: BAI1 may play a previously unappreciated role as a regulator of synaptic function. © 2013 by The American Society for Biochemistry and Molecular Biology, Inc.