An epidermoid cyst located in the true intracavernous sinus is extremely rare. A 22-year-old man presented with right ophthalmoplegia that had developed 3 years previously. The computed tomography (CT) and magnetic resonance (MR) images demonstrated a mass in the right cavernous sinus. The mass was a non-enhancing cystic lesion with a focal high density portion seen on the CT scan. The lesion displayed a markedly hyperintense signal on the diffusion-weighted images (DWI) and a heterogeneously hyperintense signal on the constructive interference in the steady state (CISS) images, which was all consistent with an epidermoid cyst. On the operation field, the mass was noted to be a true intracavernous sinus lesion, and it was histopathologically confirmed to be an epidermoid cyst.