A 43-year-old man with Behçet's disease developed a left oculomotor palsy and a right elevation paresis. His clinical picture was consistent with an isolated fascicular third cranial nerve palsy, considering the mass effect of a large left capsulothalamic lesion extending down into the mesencephalon, which was visualized by CT and (more precisely) by MRI. The patient's clinical status was improved with steroid and immunosuppressive therapy, and radiologic abnormalities resolved markedly in a month.