Visualization of the superior ophthalmic vein (SOV) on carotid angiography was investigated based on a prospective sample of 452 carotid angiograms performed during one year. The SOV with normal blood flow direction, from facial veins into the cavernous sinus (CS), was seen on 26% and with reversed flow direction in 7% of the angiograms. A hypothesis was suggested that the anatomical variations of the middle cerebral (MCV) and uncal veins (UV) affected the visualization. When both the MCV and UV drained into the CS, the SOV was seen in 11% of 179 angiograms. If the MCV and UV bypassed the CS, the SOV was seen on 51% of 118 angiograms. The difference is significant. Intubation of the patient increased the visualization of the SOV with normal flow direction but did not affect the visualization of the SOV with reversed flow. No SOV with normal blood flow direction was seen on selective internal carotid angiogaphy.