&NA;The increasing use of microsurgical decompression for trigeminal neuralgia has created a need for more detailed anatomical information about the approach. To define better this anatomy, 10 cerebellar specimens obtained at autopsy were examined, and intraoperative findings in 30 patients with trigeminal neuralgia were analyzed. Since the infratentorial subdural space on the tentorial cerebellar surface is exposed to explore the trigeminal nerve in the infratentorial lateral supracerebellar approach, attention was directed to the following: the anterolateral margin of the cerebellar hemisphere, bridging veins on the tentorial surface, superior petrosal veins, and relationships between blood vessels and the trigeminal nerve. The lateral mesencephalic segment of the superior cerebellar artery at or near the bifurcation often compressed the nerve laterally at more than one point. With this approach, the relationship of the superior cerebellar artery to the nerve could be observed from the medial side of the tentorial surface. The infratentorial lateral supracerebellar approach is discussed and compared to Dandy's cerebellar route. (Neurosurgery24:890‐895, 1989)