Raeder’s syndrome, or paratrigeminal oculosympathetic syndrome, is a rare cause of unilateral headache characterized by the association of unilateral pain and partial Horner’s syndrome. This chapter presents a case of a patient with severe unilateral headache, ptosis, and miosis, in whom neuroimaging revealed an internal carotid artery dissection with a pseudoaneurysm in the paraclinoid segment, consistent with a structural etiology for Raeder’s syndrome. The historical background of the syndrome, its pathophysiology, diagnostic approach, and management are discussed, with emphasis on neuroimaging and the role of carotid pathology.