Background: Migraine is a prevalent disease which is classified into two groups of migraine with aura and without aura. Eighteen percent of women and 6.5 percent of men in United States have migraine headache. Migraine headache is prevalent in all age groups but it usually subsides in adults above fifty. Migraine has many risk factors such as stress, light, tiredness, special foods and beverages. The aim of this study was the evaluation of the effects of body mass index (BMI) on the treatment of migraine headaches.Methods: All patients assigned to four groups according to their BMI. Patients with more than three attacks per month received nortriptyline and propranolol for eight weeks. The frequency, duration and severity of pain were measured by visual analogue scale (VAS) and behavioral rating scale (BRS-6) in regular intervals.Results: 203 patients completed the study. 153(75%) subjects were women and 50(25%) were men. Mean age of patients was 30.5 ± 7.1 years. Mean weight was 80.4 ± 14.1 kg and mean height was 1.67 ± 0.07 m. Pain frequency and duration showed statistically significant differences among four groups with better response in patients with lower BMI (P < 0.0001). VAS and BRS-6 scales showed statistically significant differences among four groups in favor of patients with lower BMI (P < 0.0001).Conclusion: This study showed that obesity has a direct influence on the treatment of migraine headaches. It could be recommended to patients to reduce their weight for better response to treatment. In addition, care should be taken about migraine drugs which make a tendency for increased appetite.