Of 59 adults admitted to Bellevue Hospital, New York, between 1968 and 1979 because of hypothermia due to exposure, 24 (41%) had 32 serious infections. Nine infections were not diagnosed at the time of admission. Infected patients warmed to higher peak temperatures were more likely to be comatose and had lower lymphocyte counts. At admission, physicians gave antibiotics to only one of nine patients with occult infection but to ten of 35 uninfected patients, thus failing to identify which patients required prompt antibiotic therapy. Delay in therapy contributed to the death of two patients. Since infection is frequently masked in hypothermic patients, careful repeated evaluations should be carried out to identify early infections. Although the proper use of antibiotics in patients with hypothermia is unresolved, we believe that prompt empiric antibiotic therapy is appropriate.