PURPOSE: To evaluate the MR findings of septic thrombosis of the cavernous sinus. MATERIALS AND METHODS: Eleven MR images of six patients with septic cavernous sinus thrombosis obtained over a five-year period and proven clinically or radiologically were retrospectively reviewed. The contour and enhancement pattern of the cavernous sinus, changes in the internal carotid artery, orbit, pituitary gland and sphenoid sinus, and intracranial abnormalities were analyzed and compared with the findings of follow-up studies. RESULTS: In all six patients, contrast study revealed asymmetrical enlargement of the ipsilateral cavernous sinus and multiple irregular filling defects within it. Narrowing of the cavernous portion of the ipsilateral internal carotid artery was noted in five patients, upward displacement of the ipsilateral internal carotid artery in four, ipsilateral proptosis with engorgement of the superior ophthalmic vein in two, pituitary enlargement in five, and inflammatory change in the sphenoid sinus in six. Associated intracranial abnormalities included edema and enhancement in the meninx, temporal lobe, or pons adjacent to the cavernous sinus in four patients, hydrocephalus in one, and cerebral infarction in one. Follow-up MR imaging indicated that the extent of asymmetrical enlargement of the cavernous sinus, filling defects within it, as seen on contrast study, and enlarged pituitary glands had all decreased, without significant interval change. CONCLUSION: MR imaging is useful in the diagnosis of septic cavernous sinus thrombosis. Asymmetrical enlargement of the cavernous sinus, multiple irregular filling defect within it, as seen on contrast study, and changes in the internal carotid artery are characteristic findings.