The CA2 region of the hippocampus is a disynaptic gateway between the entorhinal cortex and CA1. This study showed that in adult mice, selective inactivation of CA2 pyramidal cell output resulted in the loss of memory of a previously encountered conspecific but had no effect on the amount of time spent interacting with a littermate or on hippocampus-dependent forms of spatial memory and fear memories. These findings indicate an important role for CA2 pyramidal neurons in hippocampus-dependent social memory.