PURPOSE: To describe the MRI findings of trigeminal neurinoma. MATERIALS AND METHODS: We retrospectively analyzed the MRI findings of 19 patients with trigeminal neurinomas proven by surgery and pathologic examination. Axial T1-and T2-weighted MR images in all patients and gadolinium-enhanced T1-weighted images in 14 patients were obtained at 2.0T (8 cases), 1.5T (6 cases) or 0.5T (5 cases). These were analyzed in terms of tumor size, signal intensity, degree of contrast enhancement, the presence or absence of cystic change and denervation atrophy of the masticator muscles. RESULTS: Clinical manifestations included sensory abnormality or pain (n=12), headache (n=10), impaired visual acuity or diplopia (n=6), hearing loss or tinnitus (n=3), weakness of masticator muscles (n=2), and mass or nasal obstruction (n=2). On MR images, tumor size was seen to average 4.2 (range 1.5-6)cm; tumors were located in the posterior cranial fossa (n=8), middle cranial fossa (n=4), ophthalmic nerve (n=2), maxillarynerve (n=1), and mandibular nerve (n=1), and in three cases were dumb bell-shaped and extended into both the middle and posterior cranial fossa. On T1-weighted images, signals were isointense with cortical grey matter, in ten cases (53%), and of low intensity in nine (47%); on T2-weighted images, signals were of high intensity in 15 cases (79%) and were isointense in four (21%). Cystic change was seen in 12 cases (63%). After enhancement, all (14/14) the tumors enhanced. Denervation atrophy was seen in nine cases (47%) and all of these involved the trigeminal ganglion or mandibular nerve. CONCLUSION: A trigeminal neurinoma shows similar signal intensity and enhancement to other cranial neurinomas with a higher incidence of cystic degneration. Its location and shape are characteristic, and where there is involvement of the trigeminal ganglion or mandibular nerve, denervation atrophy may be seen.