The design and evaluation of a neonatal skin surface temperature-monitoring instrument that indicates when the temperature sensor becomes loose is presented. The skin surface temperature is sensed using a standard clinical thermistor probe. Thermal contact with the skin is evaluated every 4.5 min by determining the heat dissipation properties of the probe. A 6.1-mA, 14-s pulse is applied to the thermistor and the rate of temperature rise of the sensor is determined. Differences in this rate were found when the probe was in contact with skin and when it was in air, and an electronic circuit has been designed to recognize this difference. Evaluation on ten infants in incubators demonstrated that the instrument could accurately detect probe separation from the skin in all cases. When the instrument was evaluated on ten infants in bassinets at room temperature and ten adults, alarm conditions were seen in nine of ten cases when one side of the probe was separated from the skin by a 1.0-mm gap.