This double-blind, placebo-controlled study was designed to evaluate the efficacy and tolerability of early treatment of a single migraine attack, when headache pain was mild, with two doses (20 mg and 40 mg) of eletriptan. Patients (N = 613; female 79%; mean age 39 years) meeting International Headache Society criteria for migraine were encouraged, but not required, to utilize early treatment, thus providing an opportunity to assess the relative contribution to efficacy of pain severity and timing of dose. For the total patient sample (mild-to-severe headaches), 2-h pain-free rates were significantly higher than placebo (22%) on both eletriptan 20 mg (35%; P < 0.01) and eletriptan 40 mg (47%; P < 0.0001). For the cohort of patients who treated their headache when the pain intensity was mild, the 2-h pain-free rate on eletriptan 40 mg was 68% compared with 25% on placebo (P < 0.0001). Pain intensity at the time of taking eletriptan appeared to influence outcome more than the timing of the dose relative to headache onset. Eletriptan was well-tolerated, with adverse event rates similar to placebo when mild headaches were treated.