Neuropathy of the trigeminal nerve can involve its full course, from its nuclei in the brain stem to its peripheral branches. The nerve can be divided into four segments--brain stem, cistern, the Meckel cave and cavernous sinus, and extracranial--and consideration of the pathologic entities by these locations simplifies the differential diagnosis. Multiple sclerosis, infarct, and glioma are the most common abnormalities in the brain stem leading to trigeminal neuropathy. The most common cisternal cause is neurovascular compression, followed by acoustic and trigeminal schwannomas, meningiomas, epidermoid cysts, lipomas, and metastases. Trigeminal neuropathy arising from the Meckel cave and cavernous sinus is frequently due to meningiomas, trigeminal schwannomas, epidermoid cysts, metastases, pituitary adenomas, and aneurysms. Malignant tumors, which may demonstrate perineural tumor spread, are the most common extracranial cause. Because the clinical findings do not permit accurate lesion localization, magnetic resonance imaging must be used to visualize the entire course of the fifth cranial nerve. The standard study should include T2-weighted images of the whole brain and high-resolution axial and coronal T1-weighted images of the skull base obtained with and without contrast material enhancement.