Primary erythermalgia is a rare neuropathy characterized by attacks of burning pain and redness in the extremities in response to warm stimuli. We describe here a boy with erythermalgia whose painful attacks began in infancy. We found a novel mutation of SCN9A, which is a responsible gene for primary erythermalgia in this case. In his teens, he developed wintry hypothermia with resultant neurological dysfunction and recurrent pneumonia. During the course of pneumonia, he had transient encephalopaty with a reversible lesion in the splenium of the corpus callosum. In addition to excessive cooling, a defect in central thermoregulation may have caused hypothermia in this patient.