The aims of this study were to establish Doppler criteria for identifying direct carotid-cavernous fistulae (DCCF), as well as the level of agreement between results obtained by Doppler mapping vs. angiography. Doppler mapping and angiography were used to assess the direction of flow in the superior ophthalmic veins and the resistivity index in the internal carotid arteries of 30 patients with DCCF. Both methods independently demonstrated reverse flow in superior ophthalmic vein ipsilateral to the DCCF in 22 patients and normal flow in another four. The mean resistivity index for internal carotid arteries with ipsilateral DCCF was significantly reduced (p = 0.0001) compared with that for contralateral internal carotid arteries without DCCF. A resistivity index value of 0.495 offered a sensitivity and specificity of 86.6% in diagnosing ipsilateral DCCF. These findings suggest that a resistivity index < 0.495 in the ipsilateral internal carotid artery, with or without reverse flow in the superior ophthalmic vein, is associated with a reasonable probability of diagnosing DCCF.