Spontaneous dissection of the internal carotid artery is not well known in Scandinavia. Several hundred cases have been reported world-wide, but none from Finland. We presume the annual incidence in Finland to be at least 20-30 cases, nearly all of which remain undiagnosed. Our experience of 12 cases indicates that the typical patient is a middle-aged man who after strenuous physical exertion suffers a transient ischemic attack or progressing stroke. Manifestations may include ipsilateral incomplete Horner's syndrome and facial or cervical pain. The diagnosis is based on angiography and verified from repeat angiograms. The most typical finding is an extracranial stenosis or occlusion of the internal carotid artery. Irregular expansion, double lumen and aneurysmal dilation are also fairly common. The stenotic area usually recanalizes in a few months. Nonsurgical management is recommended. Prompt diagnosis and adequate heparinization with simultaneous start of oral anticoagulation seem to give the best final result.