A morphometric study on the trigeminal ganglion and the intracranial portion of the ophthalmic, maxillary and mandibular nerves was done in 50 Korean adult cadavers. The shape of the ganglion was classified into 7 types and semicircular shape was most common (54%). Mean width of the trigeminal root at porus trieminus was 6.08mm. The length of the trigemnal root from porus to the trigeminal ganglion was 8.28mm at ophthalmic portion, 10.16mm at maxillary portion, and 8.90mm at mendibular portion. Maximum width of the ganglion was 15.48mm and the breadth of the ophthalmic, and maxillary portion were 5.25mm and 5.26mm, respectively, and that of the mandibular portion (4.92mm) was narrow than the other portion. Intracranial ophthalmic nerve was 4.30mm of width and 17.89mm of length, and this nerve inclined average 39.7。 (range 14.56。) from sagital plane. It was observed infrequently that the cavernous sinus extended to the lateral border of the maxillary nervw and the emissary sinus ran under the mandibular nerve.