In 2012, a 69-year-old man noticed slowness in his movements and was diagnosed with Parkinson's disease (PD). In December 2017, he was admitted to a hospital with a diagnosis of hypothermia. One month later, in January 2018, he had difficulty moving around at home and was admitted to our hospital because of impaired consciousness. On admission, his consciousness was rated as level II-10, his body temperature was 32.8℃, and he was pale and had extrapyramidal symptoms. Electrocardiogram showed T-wave flattening and the first degree of atrioventricular block. Warming was started with improvement of the level of consciousness on the sixth hospital day. His cognitive function was normal (HDS-R 27/30), but the Schellong test (an orthostatic blood pressure test) showed a marked decrease in systolic blood pressure upon standing. Although sympathetic skin and flow responses were almost normal, except for low levels of basal skin blood flow, we speculated that the patient had impaired thermoregulation due to central autonomic dysfunction. In the literature, such impaired thermoregulation was suggested as the cause of hypothermia in seven patients with PD. Therefore, we recommend that patients with PD and repeated hypothermia should be instructed to maintain a suitable room temperature and to dress warmly. (Received 25 June, 2021; Accepted 31 August, 2021; Published 1 December, 2021).