A 32-year-old man received a total of 480 injections of subcutaneous sumatriptan 6 mg for the treatment of acute attacks of chronic cluster headache over an eleven-month period. Over 90% of the attacks resolved within 10 min of treatment (average 6.8 +/- 3.4). As a comparison, the average duration of 61 attacks occurring over the same period, but not treated with sumatriptan, was 56.1 +/- 20.8 min. This difference was highly significant. There was no clinical evidence of tachyphylaxis, and there were no adverse effects. This is the first report of a long-term treatment of cluster headache with sumatriptan. It is concluded that sumatriptan in this case was an effective and well-tolerated treatment for cluster headache.