Cluster headache is a rare yet exquisitely painful primary headache disorder occurring in either episodic or chronic patterns. The unique feature of cluster headache is the distinctive circadian and circannual periodicity in the episodic forms. The attacks are stereotypic--they are of extreme intensity and short duration, occur unilaterally, and are associated with robust signs and symptoms of autonomic dysfunction. Although the pathophysiology of cluster headache remains to be fully understood, there have been a number of recent seminal observations. To exclude structural mimics, patients presenting with symptoms suggestive of cluster headache warrant at least a brain magnetic resonance imaging (MRI) scan in their work-up. The medical treatment of cluster headache includes acute, transitional, and maintenance prophylaxis. Agents used for acute therapy include inhalation of oxygen, triptans, such as sumatriptan, and dihydroergotamine. Transitional prophylaxis refers to the short-term use of fast-acting agents. This typically involves either corticosteroids or an occipital nerve block. The mainstay of prophylactic therapy is verapamil. Yet, other medications, including lithium, divalproex sodium, topiramate, methysergide, gabapentin, and even indomethacin, may be useful when the headache fails to respond to verapamil. For medically refractory patients, surgical interventions, occipital nerve stimulation, and deep brain stimulation remain an option. As the sophistication of functional neuroimaging increases, better insight into the pathophysiological mechanisms that underlie cluster headache is expected.