The efficacy, safety, and tolerability of subcutaneous sumatriptan in the acute treatment of cluster headache were investigated in a multicenter study over a period of up to 1 year. A total of 2,031 attacks were evaluated in 52 patients. Therapy was successful in 88% of all attacks. Freedom from pain within 15 minutes in more than 90% of all attacks treated was reported by 42% of the patients, and no decline in efficacy occurred during the course of the study. Adverse events were reported by 62% of the patients.