偏头痛（英语：Migraine）是一种出现反复轻度或重度头痛的慢性疾病，通常伴有各种自主神经系统症状。偏头痛的英文“Migraine”一词源于希腊语ἡμικρανία（hemikrania），意为“头部一侧的疼痛”， 其中，ἡμι- （hemi-），意为“一半”，κρανίον（kranion），意为“颅骨”。

通常这种头痛为单侧性质（仅涉及一侧头部），并伴有搏动，可持续2-72小时。相关症状可能包括恶心、呕吐、恐光（对光线更加敏感）、恐声（对声音更加敏感），且肢体活动会加重疼痛的感觉。 三分之一的偏头痛患者均能感到病症先兆：短暂的视觉、感觉、语言或肢体障碍都意味着头痛即将发作。

Migraine is a primary headache disorder characterized by recurrent headaches that are moderate to severe. Typically, the headaches affect one half of the head, are pulsating in nature, and last from two to 72 hours. Associated symptoms may include nausea, vomiting, and sensitivity to light, sound, or smell. The pain is generally made worse by physical activity. Up to one-third of people have an aura: typically a short period of visual disturbance which signals that the headache will soon occur. Occasionally, an aura can occur with little or no headache following it.