A practical reference and educational tool that teaches headache specialists, neurologists and those who provide care to patients with headache about the comorbid illnesses they will encounter in their patients. Headache Medicine is increasingly recognized as a dedicated specialty with an emerging cohort of physicians focused on treating these patients. Given the high prevalence of headache globally, patients often have comorbid conditions, which affect treatment decisions and outcomes in innumerable ways. This easy-to-use reference of comorbid conditions facilitates an understanding of the complete patient with a headache. Each chapter discusses the longitudinal illnesses organized by body system, in addition to chapters on general internal medicine and the treatment of special populations. Headache clinicians will benefit from building knowledge of general internal medicine topics as an overlay to their headache practice. This reference of comorbid conditions supports a holistic approach to the patient with a headache. In addition to headache specialists, it will benefit a wide range of health care providers, including neurologists, primary care physicians, subspecialists, and gynecologists.