The objective was to evaluate the efficacy and tolerability of oral sumatriptan (100 mg) in patients who self–reported with menstrually related migraine. A prospective, multicentre, randomised, double–blind, placebocontrolled, two–group crossover study was carried out in 20 UK primary and secondary care surgeries. Of 115 patients with a self–reported history of menstrually related migraine that entered the study, 93 patients completed it. Patients treated all migraine attacks for 2 months with sumatriptan (100 mg) and for 2 months with placebo. The primary endpoint was the proportion of patients reporting headache relief at 4 hours for the first treated attack. Only 11% of patients fulfilled the protocol definition of menstrually related migraine. Patients reported a variable pattern of migraine attacks occurring inside and outside the menstrual window. For the first attack, significantly more patients receiving sumatriptan than placebo reported headache relief for attacks occurring inside (67% vs. 33%, p=0.007) and outside (79% vs. 31%, p<0.001) the menstrual period. Sumatriptan was generally well tolerated. Oral sumatriptan (100 mg) is an effective and well tolerated acute treatment for patients who report menstrually related migraine.