Fatigue is a common symptom frequently reported in many disorders including headaches, but little is known about its nature. The objective was to determine the prevalence of fatigue in chronic migraine (CM) patients, to define its subtypes and its relationship with other conditions comorbid with CM. Sixty-three CM patients were analysed. The Fatigue Severity Scale (FSS), the Chalder fatigue scale and the CDC diagnostic criteria for chronic fatigue syndrome (CFS) were used. Fifty-three (84.1%) patients had FSS scores greater than 27. Forty-two (66.7%) patients met the CDC criteria for CFS. Thirty-two patients (50.8%) met the modified CDC criteria (without headache). Beck depression scores correlated with FSS, mental and physical fatigue scores. Trait anxiety scores also correlated with fatigue scales. Women had higher FSS scores than men, P < 0.05. Physical fatigue was associated with fibromyalgia, P < 0.05. Fatigue as a symptom and CFS as a disorder are both common in CM patients. Therapeutic interventions include a graded aerobic exercise program, cognitive behavioural therapy and antidepressants. Identification of fatigue and its subtypes in headache disorders and recognition of headaches in CFS patients has implications for the pathophysiology, diagnosis and treatment of these disorders.