Introduction: Migraine and subclinical hypothyroidism (SCH) are common medical diseases, both share similar pathophysiological changes. Aims: To estimate the frequency of SCH among migraine patients and to evaluate the impact of SCH on migraine as regard severity and disability. Methods: Using a case control strategy, 130 patients with migraine and 130 healthy control subjects were recruited. Measurement of thyroid hormones levels was done for all the participants. Numerical Pain Rating Scale (NPRS) was used to detect the intensity of pain. Migraine severity and disability in different activity domains were assessed by Migraine Severity Scale (MIGSEV) and Headache Disability Index (HDI), respectively and patients' response to migraine treatment was evaluated by Headache Under-Response to Treatment Questionnaire (HURT). Results: The frequency of SCH was significantly higher among migraine patients than control subjects (p=0.002; OR=2.89; at 95% CI). Intensity of pain and migraine disability were significantly high in migraine patients with SCH when compared to migraine patients without SCH (p=.0001, p= 0.01, respectively). Most of migraine patients with SCH had grades II and III of MIGSEV scale (p=0.01, p= 0.04). The control of migraine was not good in 44.8% of the group with SCH versus 19.4% of the group without SCH (p=0.005). Conclusions: Subclinical hypothyroidism is more frequent among patients with migraine in respect to control subjects. Moreover, SCH has negative impacts on migraine regarding severity and disability.