Cancer can affect the autonomic nervous system in a variety of ways: direct tumor compression or infiltration, treatment effects (irradiation, chemotherapy), indirect effects (e.g., malabsorption, malnutrition, organ failure, and metabolic abnormalities), and paraneoplastic/autoimmune effects. This chapter focuses on a diagnostic approach and treatment of cancer patients with dysautonomia, with an emphasis on immune-mediated autonomic dysfunction, a rare but potentially highly treatable cause of dysautonomia. Autonomic dysfunction can be divided into nonneurogenic (medical) and neurogenic (primary or secondary) causes. Orthostatic hypotension is a cardinal symptom of dysautonomia. The autonomic testing battery includes sudomotor, vasomotor, and cardiovagal function testing and defines the severity and extent of dysautonomia. Conditions encountered in the cancer setting that are associated with autonomic dysfunction include Lambert-Eaton Myasthenic Syndrome, anti-Hu antibody syndrome, collapsin response-mediator protein 5, subacute autonomic neuropathy, neuromyotonia (Isaacs’ syndrome), and intestinal pseudo-obstruction. The chapter describes various pharmacologic and nonpharmacologic therapies for treatment of orthostatic hypotension.