The aim of the open prospective study was to investigate the efficacy, safety and tolerability of subcutaneous sumatriptan in the acute treatment of cluster headache. Self-treatment with 6 mg sumatriptan subcutaneously was monitored over a period up to 1 year. Headache parameters were documented by the patients with a headache diary. A total of 2031 attacks in 52 patients were investigated. Treatment with sumatriptan was effective in 88% of the attacks and 57% of the patients were pain-free within 15 min after injection; 42% of the patients became painfree within 15 min after at least 90% of their attacks. During long-time treatment the efficacy remained unchanged. Of the patients 10% withdrew from the study due to lack of efficacy or adverse events. In total, 62% of the patients reported adverse events, which were serious in 3.8% of the cases. Subcutaneous self-treatment of cluster headache is both highly effective and well tolerated.