First symptoms and initial clinical, ultrasonographic and neuroradiological findings ascertained a mean of 5.6 days (SD = 5.6 days), 7.7 days (7.0), and 11.2 days (8.0) after symptom onset were analysed in 44 patients who suffered a spontaneous internal carotid artery dissection (ICD) verified by magnetic resonance imaging, angiography, or both. Common symptoms signalling dissection were unilateral headache in 68%, transient ischaemic attack in 20%, and cerebral infarction in 9%. Severe pain preceded cerebral ischaemia by more than 3 days in 60% of those patients who eventually suffered a stroke. However, only 2 were admitted because of pain alone and 33 for evolving neurological deficits. During the first month, ipsilateral severe headache occurred in 89%, neck pain in 36%, ipsilateral cerebral ischaemia in 82%, ocular ischaemia in 16%, oculosympathetic palsy in 48%, and cranial nerve palsy in 5%. Recent "trivial" head or neck trauma was elicited in 41%. Doppler and duplex sonography confirmed the clinical suspicion of ICD in 91.5% and in 96% of those with a significant stenosis or occlusion. MRI demonstrated a thickened vessel wall in all 33 imaged carotid dissections and a mural haematoma in 30. None of the 32 patients who received anticoagulant treatment subsequently deteriorated. Monitoring anticoagulant treatment with ultrasonographic follow-up studies demonstrated recanalization in 70% and persistent occlusion in 30%. The results demonstrate that familiarity with the initial symptoms, especially headache, and performance of an ultrasonographic study without delay are the cornerstones of an early diagnosis.(ABSTRACT TRUNCATED AT 250 WORDS)