This study determined the utility and accuracy of susceptibility-weighted MRI (SWI) for the detection of carotid cavernous fistulas. We retrospectively compared SWI images in nine patients (Group 1, case group) of DSA-proved carotid cavernous fistula (CCF) and 19 DSA negative cases for CCF as a control group (Group 2). Group 1 was again sub-grouped into direct and indirect types. Using uniform region-of-interest measurements, signal intensity within the superior ophthalmic vein (SOV) and the superior sagittal sinus (SSS) were measured on magnitude images of SWI. The SOV/SSS signal intensity ratio was calculated in each case and the mean values of the two groups were compared. Eleven SOV/SSS signal intensity ratios in Group 1 (7 unilateral and two bilateral CCF), 38 in Group 2 (both sides in 19 control subjects) were included. Median ± interquartile range of SOV/SSS ratios for Group 1, Group 2, indirect and direct type CCFs were 1.07 ± 0.43, 0.39 ± 0.23, 0.83 ±0.29, 1.4 ±0.38 respectively. Mann-Whitney test between Groups 1 and 2 was statistically significant with P<0.0001. All cases and controls were reliably distinguished with SOV/SSS signal intensity ratio of 0.64 as cut-off. Direct CCF cases had consistently higher ratios than indirect CCF. SWI was highly sensitive for detection and differentiation of both direct and indirect CCF. Only one case of corticovenous reflux was missed by SWI. SWI is useful for detection of CCF and to differentiate between direct and indirect CCF.