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.