Raeder first described Horner's syndrome with ipsilateral head pain due to paratrigeminal organic disease, but most subsequent reports of this syndrome were idiopathic. Our recent case prompted a review of past reports of idiopathic Raeder's syndrome. Because in recent years the features of Raeder's syndrome have been recognized as common manifestations of carotid artery dissection, we divided the cases into those with and those without carotid imaging studies. The classifications and differential diagnoses are discussed. Sixteen cases with carotid imaging studies were not very different from the 28 cases without such studies. Most studies were performed several weeks after onset of symptoms and carotid dissection could not be definitely excluded in any case. In most cases of idiopathic Raeder's syndrome, carotid artery dissection was not considered and in no case was that condition definitively excluded. People with Raeder's syndrome not associated with a paratrigeminal organic lesion probably have a disease of the carotid artery. Because of the different criteria and classifications of Raeder's syndrome it is best to relegate this eponym to history.