The incidence of hypothermia (axillary temperature less than 35 degrees C) on admission of an infant to a neonatal intensive care unit was retrospectively analyzed in 559 very-low-birth-weight (less than 1500 gm) newborn infants. The smaller infants were at greater risk of hypothermia. Only in the larger neonates was mortality related to hypothermia, which suggests that this known association bears little cause-effect relationship.