This study was designed to assess factors associated with afterdrop, the fall in core temperature following completion of cardiac surgery, and determine the validity of noninvasive measures of temperature to predict core temperature in the severely hypothermic patient. Twenty-five postcardiac surgery patients served as subjects. Core temperature was measured using the pulmonary artery, bladder, and esophageal sites. The less invasive measures included a tympanic membrane thermometer, oral and axillary electronic thermometers, and a forehead surface temperature indicator. Temperatures were recorded every 10 minutes for 2 hours. End-of-surgery temperatures ranged from 30.3–38.3° (86.5–100.9°) with a mean of 36.02 ° (96.84 °). Temperature change over the next hour ranged from a rise of 2.5 ° (4.5 °) to a fall of 4.1 ° (7.2 °). Factors associated with afterdrop included age, end-of-surgery temperature (both positively) and body mass (negatively). No noninvasive measure appeared to be a valid indicator of core temperature in these hypothermic patients.