Objectives. - The aim of this study is to assess the comprehensibility, internal consistency, patient-physician reliability, test-retest reliability, and validity of Turkish version of Migraine Disability Assessment (MIDAS) questionnaire in patients with headache. Background. - MIDAS questionnaire has been developed by Stewart et al and shown to be reliable and valid to determine the degree of disability caused by migraine. Design and Methods. - This study was designed as a national multicenter study to demonstrate the reliability and validity of Turkish version of MIDAS questionnaire. Patients applying to 17 Neurology Clinics in Turkey were evaluated at the baseline (visit 1), week 4 (visit 2), and week 12 (visit 3) visits in terms of disease severity and comprehensibility, internal consistency, test-retest reliability, and validity of MIDAS. Since the severity of the disease has been found to change significantly at visit 2 compared to visit 1, test-retest reliability was assessed using the MIDAS scores of a subgroup of patients whose disease severity remained unchanged (up to ±3 days difference in the number of days with headache between visits 1 and 2). Results. - A total of 306 patients (86.2% female, mean age: 35.0 ± 9.8 years) were enrolled into the study. A total of 65.7%, 77.5%, 82.0% of patients reported that "they had fully understood the MIDAS questionnaire" in visits 1,2, and 3, respectively. A highly positive correlation was found between physician and patient and the applied total MIDAS scores in all three visits (Spearman correlation coefficients were R = 0.87, 0.83, and 0.90, respectively, P < .001). Internal consistency of MIDAS was assessed using Cronbach's α and was found at acceptable (>0.7) or excellent (>0.8) levels in both patient and physician applied MIDAS scores, respectively. Total MIDAS score showed good test-retest reliability (R = 0.68). Both the number of days with headache and the total MIDAS scores were positively correlated at all visits with correlation coefficients between 0.47 and 0.63. There was also a moderate degree of correlation (R = 0.54) between the total MIDAS score at week 12 and the number of days with headache at visit 2 + visit 3, which quantify headache-related disability over a 3-month period similar to MIDAS questionnaire. Conclusion. - These findings demonstrated that the Turkish translation is equivalent to the English version of MIDAS in terms of internal consistency, test-retest reliability, and validity. Physicians can reliably use the Turkish translation of the MIDAS questionnaire in defining the severity of illness and its treatment strategy when applied as a self-administered report by migraine patients themselves.