Prostatic perineural structures were studied by electron microscopy in 31 specimens from benign and malignant lesions. Vascular structures seen in these areas have the ultrastructural characteristics of blood capillaries. No lymphatic channels were observed. Spread of tumor cells occurred by direct extension around the prostatic nerves and not within vascular channels. It is possible that these perineural spaces represent areas of least resistance to tumor invasion. These findings were not reported in previous studies on the ultrastructure of the human prostate.