The hippocampus contains a heterogeneous population of interneurons. Parvalbumin (PV) positive neurons constitute an abundant subpopulation of cells that express GABA. The authors observed PV immunoreactivity in the hippocampal CA1 region and dentate gyrus of variously aged dogs. In 1-year-old dogs, PV immunoreactive neurons were detected in the stratum oriens of the CA1 region, and in the polymorphic layer of the dentate gyrus. In addition, weak PV immunoreactive fibers were observed in all layers in the CA1 region and dentate gyrus. In 3-year-old dogs, PV immunoreactivity was significantly higher in the CA1 region and dentate gyrus, and this was maintained in 10-year-old dogs. This finding suggests that PV immunoreactive interneurons may show high resistance to age-dependent neurodegenerative processes.