OBJECTIVE: There is minimal detailed information regarding the sphenoparietal venous sinus found in the extant medical literature. Furthermore, there is controversy in the literature regarding drainage of the Sylvian vein into this sinus. The sphenoparietal sinus can potentially be encountered with cranial base approaches near the lesser wing of the sphenoid bone and may be found as one surgically traverses the superior orbital fissure. METHODS: To further elucidate the anatomy of this structure, we injected this intracranial venous sinus with blue latex in 15 adult cadavers (30 sides) via cannulation of the cavernous sinus near the posterior part of the oculomotor trigone. Observations and measurements of this and nearby structures were then made. RESULTS: A left and right sphenoparietal sinus were found in all specimens and had a mean diameter of 2.5 mm for left sides and 3 mm for right sides. No statistical difference was noted between sides or sexes (P > 0.05). This structure generally began at the lateral tip of the lesser wing of the sphenoid bone and ended in the cavernous sinus near the passage of the ophthalmic nerve. In seven left sides and eight right sides, no discernible connection with the middle meningeal veins was noted. This sinus was found to have a connection with the Sylvian vein in all but one side. One sinus did not drain into the cavernous sinus but rather into the veins of the foramen rotundum. Ten specimens were noted to have previously undocumented temporal veins from the anterior temporal tip that drained into the sphenoparietal sinus. CONCLUSION: We think that these data will aid the clinician in the diagnosis of the pathology of this region and decrease morbidity that may follow manipulation of this venous sinus. Copyright © by the Congress of Neurological Surgeons.