Objective. To analyze the prevalence, causes and outcome of hypothermia in institutionalized elderly. MethOds. Prospective study held from January to December, 2004 at Hospital Geriátrico e de Convalescentes Dom Pedro II, with 483 long-term care patients. Hypothermia was diagnosed by esophageal thermometer in all patients with axillary temperature below or equal to 35°C (95°F). Both etiologic diagnosis and complications from hypothermia were noted in clinical and subsidiary examinations. Tests included: ECG, chest radiography, blood count, blood gas analysis, glycemia, metabolites, biochemical blood tests, amylase, kidney and liver functions, urinalysis and serology for HIV, syphilis and hepatitis B. Rewarming was adopted, among other actions in the treatment protocol. Results. Prevalence of hypothermia was 7.2 percent, and the condition was found most often in women (65.7%). The mean age in the sample was 76.4 years. Most patients (77.1%) had high degrees of dependence (Katz index "F" and "G"). Mild hypothermia was identified for most (71.4%) patients. The mortality rate was 62.8 percent, 31.4 percent during hypothermia and 31.4 percent after reversal. Infections were the etiology in all cases: pneumonia (80.0%), urinary tract infection (60.0%), and pressure ulcer (17.1%). There was more than one infection for the same patient in 60 percent of cases. cOnclusiOn. Hypothermia in institutionalized elderly is a serious clinical condition with high rates of mortality. Prevention, early diagnosis and measures of core rewarming improve prognosis.