Objective: To determine the efficacy of oral rizatriptan 10 mg and 5 mg for treating menstrually associated migraine attacks. Methods: Data from two large clinical trials with identical designs were included in a retrospective analysis. The studies were randomized, double-masked, placebo-controlled, incomplete block, two-period, crossover designs. Women with migraines were randomly assigned to one of five treatment sequences for the treatment of two migraine attacks. Only data from the first attack in women with migraines who were treated with rizatriptan or placebo were included in the analysis. A menstrually associated attack was defined as one that occurred within 3 days before or after the onset of the last menstrual period. Results: In the subgroup of 335 women with menstrually associated migraine, rizatriptan was effective compared with placebo. At 2 hours after dosing, 68% of 139 women taking rizatriptan 10 mg and 70% of 115 women taking rizatriptan 5 mg with a menstrually associated migraine had pain relief compared with 44% of 81 patients taking placebo (P < .05). In all women, rizatriptan was as effective in treating menstrual as well as nonmenstrual migraine: 68% of 139 patients taking rizatriptan 10 mg with a menstrually associated migraine had pain relief at 2 hours after dosing compared with 69% of 393 patients with nonmenstrually associated attacks (test of menstrual association = nonsignificant; the analysis had 80% power to detect a difference of six percentage points between groups). Similar results were found for rizatriptan 5 mg (menstrual = 70%, nonmenstrual = 66%; not statistically significant). Conclusion: Rizatriptan is effective in the treatment of menstrually associated migraine attacks.