Previous reports have indicated morphologic hippocampal asymmetry in thickness in male and female rats. In the present study, the possible sex differences and right-left asymmetries in rat hippocampal components were investigated. Pyramidal cells in four hippocampal sectors on thionin-stained sections were counted and the thickness of the hippocampal components was measured on microslide-projected images. The present study showed significant sexual dimorphism in two hippocampi as well as asymmetry in male. These findings agree with those found in humans.