Primary cluster headache (CH) is an excruciatingly severe pain condition. Several pharmacologic agents are available to treat chronic CH, but few double-blind, randomized clinical trials have been conducted on these agents in recent years, and the quality of the evidence supporting their use is often low, particularly for preventive agents. We recommend sumatriptan or oxygen to abort ongoing headaches; the evidence available to support their use is good (Class I). Ergotamine also appears to be an effective abortive agent, on the basis of experience rather than trials. We consider verapamil and lithium to be first-line preventives for chronic CH, although the trial evidence is at best Class II. Steroids are clearly the most effective and quick-acting preventive agents for chronic CH, but long-term steroid use carries a risk of several severe adverse effects. We therefore recommend steroids only if verapamil, lithium, and other preventive agents are ineffective. In rare cases, patients experience multiple daily cluster headaches for years and are also refractory to all medications. These patients almost always develop severe adverse effects from chronic steroid use. Such patients should be considered for neurostimulation. Occipital nerve stimulation is the newest and least invasive neurostimulation technique and should be tried first; the evidence supporting its use is encouraging. Hypothalamic stimulation is more invasive and can be performed only in specialist neurosurgical centers. Published experience suggests that about 60% of patients with chronic CH obtain long-term benefit with hypothalamic stimulation.