That sumatriptan tablets are effective and well tolerated in the acute treatment of migraine has been established, but the relationship between dose and efficacy has not been adequately defined to date in clinical trials. This multinational double-blind trial (N = 1003) in which patients treated up to three migraine attacks with sumatriptan 25 mg, 50 mg, 100 mg, or placebo, with a second independently randomized dose for headache recurrence, evaluated the efficacy and tolerability of three doses of sumatriptan. The results demonstrate that all doses of sumatriptan were superior (P < 0.05) to placebo in reducing moderate or severe predose headache to mild or no headache 4 hours postdose for each of the three treated attacks; sumatriptan 50 mg and 100 mg were each superior (P < 0.05) to sumatriptan 25 mg 4 hours postdose for two of three attacks. Sumatriptan (all doses) was similarly effective at relieving nausea and photophobia or phonophobia or both and at reducing clinical disability. Headache recurrence was experienced by similar proportions of patients across treatment groups (35% to 48% after placebo; 26% to 39% after sumatriptan). Relief of recurrent headache 2 hours after the second dose of study medication occurred in greater percentages of patients using any dose of sumatriptan compared with patients using placebo to treat recurrence. The incidence of adverse events with 25-mg and 50-mg sumatriptan tablets was similar to the incidence with placebo and lower than the incidence with 100-mg sumatriptan tablets. These data provide the first demonstration from a large well-controlled clinical trial that both the 50- and 100-mg doses are more effective than the 25-mg dose and that the 50-mg dose is associated with a lower incidence of adverse events than the 100-mg dose.