As patients who suffer from migraine need long-term treatment, the safety and consistent efficacy of such therapy is very important. Concurrent illness and additional medication can interfere with the treatment chosen for the attacks of migraine. The objective of this open-label study was to investigate the efficacy and tolerability of rizatriptan, in the treatment of up to three attacks of migraine, in the clinical setting. From October 1998 to July 1999, 6 174 doctors enrolled 33 147 patients into the study (26 644 women, 650 men). The mean age was 42.7 years. We were able to examine standardized migraine diaries relating to 25 501 patients and 70 537 migrainous episodes. Rizatriptan scored consistently high on efficacy and showed a consistently rapid onset. There was no evidence of tolerance to repeated use. An effect was reported within 1 hour of ingestion in 79% of attacks treated. In 27.8% of attacks, remission of headache was complete at 1 hour. Two hours after ingestion, 74% of attacks had subsided completely. Repeated administration of rizatriptan was well tolerated, and few adverse effects were seen. The most common unwanted effects were dizziness, weakness, fatigue, and nausea. No cardiovascular disturbance was seen. In the clinical setting, rizatriptan, 10 mg, is an effective and well-tolerated agent for the treatment of migraine attacks. Particularly noteworthy is the rapid onset of effect, with swift disappearance of headache. Rizatriptan has a favorable side effect profile, and, provided contraindications are observed, severe adverse cardiovascular complications are extremely unlikely.