The aim of our study was to describe anatomical variability of the root entry zone (REZ), also called the Ohersteiner--Redlich zone, that represents the "junction zone" of glia and Schwann sheath of the cranial nerves. This zone has some clinical implications. The pulsatile compression of REZ by a vessel may produce clinical symptoms, such us trigeminal neuralgia, hemifacial spasm, glossopharyngeal neuralgia torticollis spasmodicus or even symptoms of essential hypertension when a vascular crross compression of REZ of a left vagus nerve is present. The vessel - cranial nerve contact in the skull base cysterns may be visualized in radiologic examinations, most accurately in magnetic resonance imaging. Because, we cannot distinguish the REZ from the rest of the vagus nerve in radiologic examinations we decided to measure the lenght of its REZ. The microanatomical study of the lenght of REZ zone of the vagus nerve was performed on 2l nerves taken from 17 human brain stems (12 men, 5 women, 14 left, 7 right), fixed with 8% buffered, formalin solution. Paraffin embedded tissue was cut into 1O-um-thick sections pararellel to the nerve longitudinal axis and stained with hematoxilin & eosin. Each of the nerves showed the presence of a zone of oligodendrocyte myelination, mean lenght 2 ą 0.3 mm. In 17 nerves the transitional zone formred a cone-like process, in 4 nerves was shaped irregularly. The length of REZ (oligodendrocyte myelination plus "glial dome") had the mean length 3.5 ą 0,9 mm.