A 64 year old patient with a cardiac prosthesis and receiving antivitamin K therapy presented with a right bulbar syndrome. Based on absence of meningeal signs and hemorrhage on CT scan heparin therapy was instituted. Fatal coma developed two and a half days later. Autopsy findings included a right lateral bulbar infarct and meningeal hemorrhage, predominant around a fusiform dilatation of the end of the right vertebral artery. Serial sections showed a large dissecting aneurysm between media and adventitia communicating with an intimal tear. Among intracranial dissecting aneurysms those of vertebrobasilar localization have the peculiarity of being subadventitial in some cases, with a subsequent enhanced risk of hemorrhagic complications. The use of anticoagulants appears contraindicated in these cases, even if their clinical expression is suggestive of an infarct. Their etiology is often unknown.