Case report of a female patient, 58 years old, who, due to a right homonymous hemianopsia, was submitted under general anesthesia successively to angiographies through the right carotid and vertebral arteries. At the first examination no abnormalities were evidenced, but the contrast medium did not reach the posterior cerebral artery; angiography by the right vertebral artery, with extravasation of the contrast medium into the vessel wall, visualized both posterior cerebral arteries. Immediately after the angiographic study, the patient presented the characteristic picture of the Wallenberg's syndrome caused by involvement of the right lateral part of the medulla oblongata. The evolution of the case was good, despite the residual right hemifacial neuralgic pain. An involvement of the vertebral artery, through an intramural injection of Hypaque is assumed to be the most probable pathogenic mechanism. The reported complication is considered as one more warning to prevent angiographies of the vertebral artery through direct puncture of this vessel, due to its recognized anatomical variations.