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Chinchilla lanigera, is an endemic rodent inhabiting desert areas of northern Chile. We postulated that wild chinchilla should has a cost-benefit relationship in thermoregulation to cope with desert habitats. We evaluated the energy metabolism in air and He-O-2, evaporative water loss (EWL) and body temperature (T-b) at different ambient temperatures (T-a). The most relevant results indicated that the basal metabolic rate (BMR) was 0.66 mlO(2)/g h and a thermal conductance (C) of 0.0376 mlO(2)/g h degrees C; representing a 80.4% and 72.5% of expected values for eutherian mammals respectively. Thermal conductance in He-O-2 was 0.089 mlO(2)/g h degrees C, being the ratio CHe-O2/C = 0.089/0.038 equal to 2.34, the highest value recorded in rodents, indicating that C. lanigera exhibit the higher thermal insulation reported so far. Besides, the evaporative water loss (EWL) was a 95% of the expected value for heteromiyds. Chinchilla lanigera presents a clear cost-benefit relationships or tmde-off in thermoregulation. In fact, the low C and EWL values implicate thermoregulatory costs at high temperatures (risk of hiperthermia), mainly when its desert habitats has temperatures greater than or equal to 30 degrees C. At the same time these low C, EWL and BMR values represent physiological benefits that allow energy and water economy in a xeric and unproductive habitat.