Olfaction is an important and primitive sense. As its importance has changed with evolution, anatomic adjustments have occurred in its structure and vasculature. Primates are a family of vertebrates that have had to develop their visual system to adapt to the arboreal environment and have evolved from a macrosmatic to a microsmatic species as the optic system has enlarged. This has resulted in anatomic changes of a small but critical area at the base of the brain. This paper describes the three-dimensional vascular anatomy of the olfactory organ of the Japanese monkey (Macaca fuscata fuscata). This is best understood by dividing the organ into three parts: the olfactory tract, olfactory bulb, and olfactory nerves in the nasal mucosa. The bulb can be partitioned into an outer or cortical part and inner or medullary part. The vasculature and tissue were examined grossly and with light microscopy and scanning electron microscopy of vascular corrosion casts. The olfactory tract and bulb were supplied by an arteriole from the anterior cerebral artery on each side. The tract was supplied by capillaries running spirally with a coarse network. At the olfactory bulb, the arteriole ramified into the intracortical and medullary branches that formed capillary networks. The bulbar intracortical capillaries were divided into two layers with different densities and vascular patterns. The capillaries of the superficial layer had a ladder-like pattern. The branches that ran into the medulla of the olfactory bulb were more widely spaced. Twigs from the posterior ethmoidal artery ran along the nerve fiber and formed intra- and extrafascicular networks. Each region of the olfactory organ had characteristic three-dimensional vascular patterns that were related to their cellular architecture.