Frequency, magnitude, and duration of hypothermia (core body temperature less than 36.0 C) in the recovery room (RR) were determined in 198 adults. In addition, the influence of age, anesthetic technique, and shivering on the rewarming process was assessed. Tympanic membrane temperatures were recorded on admission to the RR and every 15 minutes thereafter until discharge from the RR. Sixty percent of the subjects had temperatures less than 36.0 C on admission to the RR. Elderly subjects (greater than or equal to 60 yr) had lower RR admission and discharge temperatures and experienced longer duration of hypothermia than did younger patients. General anesthesia was associated with a significantly more rapid rate of increase in postoperative temperature and a shorter duration of hypothermia than was regional anesthesia. The incidence of shivering and the incidence of hypothermia were significantly related 30 and 45 minutes after admission to the RR. Duration of hypothermia varied with different operative procedures.