BACKGROUND: Currently available measures of the efficacy of acute migraine medications are not frequently used in primary care. They may be too burdensome and complicated for routine use. OBJECTIVES: To design and test a new, easy to use, 4-item assessment tool, the Migraine Assessment of Current Therapy (Migraine-ACT) questionnaire for use by clinicians, to quickly evaluate how a recently prescribed acute medication is working, and to identify patients who require a change of their current acute treatment. METHODS: A 27-item Migraine-ACT questionnaire was developed by an international advisory board of headache specialists. Questions were formulated in four domains: headache impact, global assessment of relief, consistency of response and emotional response. All these are clinically important measures of migraine severity and treatment outcome. All questions were dichotomous and answered by yes or no. Patients (n = 185) attending secondary care headache clinics who were diagnosed with migraine according to International Headache Society criteria entered a multinational, prospective, observational study to investigate the test-retest reliability and construct validity of the 27-item Migraine-ACT. Patients completed the Migraine-ACT on two occasions, separated by a 1-week interval, and test-retest reliability was assessed by Pearson product moment and Spearman rank measures. Construct validity was assessed by correlating patients' answers to the 27-item Migraine-ACT with those to other questionnaires (individual domains and total scores) conceptually related to it; the Short-Form 36 quality of life questionnaire (SF-36), the Migraine Disability Assessment (MIDAS) questionnaire and the Migraine Therapy Assessment Questionnaire (MTAQ). Discriminatory t-tests were used to identify the four Migraine-ACT questions (one in each domain) which discriminated best between the domains of the SF36, MIDAS, and MTAQ. These four items constituted the final 4-item Migraine-ACT. RESULTS: The test-retest reliability of the 27 Migraine-ACT questions ranged from good to excellent, and correlation coefficients were highly significant for all items. The consistency of reporting the yes and no answers was also excellent. Correlations of Migraine-ACT items with SF-36 and MIDAS items and SF-36, MIDAS and MTAQ total scores indicated that the following were the most discriminating items, in the respective four domains, and constitute the final Migraine-ACT questionnaire: Consistency of response: Does your migraine medication work consistently, in the majority of your attacks? Global assessment of relief: Does the headache pain disappear within 2 h? IMPACT: Are you able to function normally within 2 h? Emotional response: Are you comfortable enough with your medication to be able to plan your daily activities? The 4-item Migraine-ACT was shown to be highly reliable (Spearman/Pearson measure r = 0.82). The individual questions, and the total 4-item Migraine-ACT score, showed good correlation with items of the SF-36, MIDAS and MTAQ questionnaires, particularly with the total MTAQ and SF-36 scores. CONCLUSIONS: The 4-item Migraine-ACT questionnaire is an assessment tool for use by primary care physicians to identify patients who require a change in their current acute migraine treatment. It is brief and simple to complete and score, and has demonstrated reliability, accuracy and simplicity. Migraine-ACT can therefore be recommended for everyday clinical use by clinicians.