The volume density of synapses in the hilus of the dentate gyrus was quantitatively assessed in adult rats. A gender difference was found, with males showing a significantly higher number of mossy fiber synapses. Other types of nerve endings on dendritic shafts and dendritic spines were not different between the two sexes. Since it has been previously shown that the volume density of mossy fiber synapses in the CA3 area of the hippocampus is higher in females than in males, the present findings suggest that the sexually dimorphic synaptic patterns may be determined not only by the presynaptic elements, but also by the postsynaptic target area.