We report a case of Tolosa-Hunt syndrome (THS) in which the lesion has been demonstrated by magnetic resonance imaging (MRI), computed tomography (CT), and angiography. A healthy 23-year-old man developed an acute painful ophthalmoplegia on the right side. CT and MRI scans revealed asymmetric enlargement of the right cavernous sinus with contrast enhancement extending down to the region of trigeminal ganglion. MRI further delineated the detailed anatomical structures of the region and excluded any infiltration of the surrounding tissues by a mass lesion. Cerebral angiography showed a significant decrease in the calibration of petrous segment and a mild decrease in the calibration of cavernous segment of the ipsilateral internal carotid artery. The patient was treated with oral prednisone, 100 mg daily. Neurological findings totally subsided after 2 weeks on corticosteroid and MRI showed resolution of the lesion in the cavernous sinus. The patient was symptom-free for 6 months after discharge. Our findings have suggested that MRI is the most valuable imaging technique for demonstration and follow-up of lesions in the cavernous sinus that are directly responsible for the symptoms of THS and the lesions can be more extensive than was currently believed.