Autonomic dysfunction in Parkinson disease encompasses thermoregulatory symptoms and was first noted by Gowers in the late 19th century when he described abnormal temperature sensation and sweating in Parkinson disease patients. These thermoregulatory symptoms became more recognized in the postlevodopa era when Parkinson disease patients were more readily tested with objective autonomic function tests. Objective thermoregulatory testing in Parkinson disease reveals deficits of sweating and vasomotor tone which often correlate with the severity of other autonomic deficits. Tests of thermoregulatory function can also be used to differentiate Parkinson disease from other neurodegenerative disorders. The pathophysiology of thermoregulatory dysfunction in Parkinson disease encompasses both central and peripheral mechanisms; involvement of the brainstem and hypothalamus with alpha-synuclein pathology is well recognized with increasing evidence of peripheral neuropathy in Parkinson disease that influences thermoregulation. Medications used to treat Parkinson disease also affect thermoregulatory symptoms. Disorders of thermoregulation significantly affect the quality of life for patients and their caregivers and can be severe and even life threatening, such as in the parkinsonism-hyperpyrexia syndrome.