It is well established that the elderly population is vulnerable to hypothermia, leading to increased morbidity. A prospective observational study took place between 1 October 1999 and 31 December 1999 in a large teaching hospital Accident and Emergency department. Core temperature was assessed at presentation using a tympanic probe on patients over 65 years of age. A total of 1543 eligible patients attended during the study period. Complete data was available on 958 patients. Forty-eight patients (5%) were found to be hypothermic (core temperature < 35 degrees Celcius). There were two peaks in hypothermic presentations; these corresponded to periods of cold weather. The incidence of hypothermia was higher in non-ambulant patients and those with co-morbidity; the majority of patients lived in relatively deprived areas by a postcode derived deprivation index. Mortality was 34% in patients hypothermic at presentation. Hypothermia contributes to mortality and morbidity in elderly patients; its incidence may be higher than previously reported.