A psychobiological model of headache is proposed which integrates the numerous aspects of headache research within a unitary conceptual framework. Central to the model is the development of a predisposition for headache that becomes more extensive and more autonomous in function as the disorder increases in severity and chronicity. Guided by the model, the present study examined the prevalence of musculoskeletal, vascular, and autonomic symptoms in a group of chronic headache patients and in a group of occasional headache sufferers. The symptoms were assessed by a 14-item questionnaire that permitted the respondents to indicate the extent to which each of the symptoms was perceived to be present across all headache attacks. In addition, a single item was included to assess the extent to which the respondents perceived their headache attacks to be a problem. The data indicated that the primary difference between the chronic and non-chronic headache sufferer was in terms of the frequency with which the different symptoms occurred rather than in terms of the kind of symptoms present. A stepwise regression analysis revealed that the symptom of nausea with the addition of four musculoskeletal symptoms accounted for 57.3% of the variance associated with the extent to which respondents perceived their headaches to be a problem. These data were interpreted as supportive of a severity model of chronic headache.