The morphology and distribution of parvalbumin-immunoreactive neurons (PV-ir) were studied in the human claustrum. PV-ir neurons were observed throughout the claustrum, with the highest numbers noted in the central (broadest) portion as compared with the dorsal and ventral aspects. Reaction product was evident in the neuronal perikarya, dendritic processes, and spines. In the majority of these labeled neurons, the cytoplasm was devoid of lipofuscin pigment. Cell bodies varied widely in both shape and size, ranging from oval and small, to multipolar and large. PV-ir neurons were classified into two groups, primarily based on dendritic morphology: spiny neurons with long and straight dendrites, and aspiny neurons with thin and curving dendritic processes. PV-ir fibers were seen throughout the neuropil, with many immuno-positive puncta noted.