Cluster headache is an uncommon yet well-defined neurovascular syndrome occurring in both episodic and chronic varieties. The most striking feature of cluster headache is the unmistakable circadian and circannual periodicity. Inheritance may play a role in some families. The attacks are of extreme intensity, of short duration, occur unilaterally, and are accompanied by signs and symptoms of autonomic dysfunction. In contrast to migraine, during an attack the cluster patient prefers to pace about. Attacks frequently occur at night. Although the pathophysiology of cluster headache remains to be fully elucidated, several seminal observations have recently been made. The medical treatment of cluster headache includes both acute therapy aimed at aborting individual attacks and prophylactic therapy aimed at preventing recurrent attacks during the cluster period. Agents used for acute therapy include inhalation of oxygen, sumatriptan, and dihydroergotamine. Transitional prophylaxis involves the short-term use of either corticosteroids or ergotamine derivatives. The cornerstone of maintenance prophylaxis is verapamil, yet methysergide, lithium, and divalproex sodium may also be employed. In some patients, melatonin or topiramate may be useful adjunctive therapies.