Cluster headache is a rare form of severe idiopathic headache characterized by unilateral short-lasting episodes of excruciating pain in association with autonomic disturbances. Subcutaneous sumatriptan has been investigated as an acute treatment for cluster headache in two randomized, double-blind, placebo-controlled, crossover trials. About 75% of patients given subcutaneous sumatriptan 6 mg reported headache relief within 15 min, in comparison with 26-35% given placebo (p < 0.001 in both studies). The need for rescue medication (100% oxygen by inhalation) at 15 min was significantly lower after sumatriptan treatment as were the severity of functional disability and incidence of non-headache symptoms. Results of a long-term study indicate that the tolera-bility and efficacy of sumatriptan 6 mg is maintained in long-term use, and that there is no evidence of tachyphylaxis.