We evaluated the influence of environmental temperature and phenotype on thermoregulation by Sceloporus palaciosi, a diurnal iguanid lizard from high elevations in central Mexico. Range of body temperature was 13–36°C with a mean of 27.82 ± 5.31°C. Active lizards had a higher body temperature than inactive ones. After removal of state of activity from analysis, sexes did not differ in body temperature. Body temperature was significantly correlated with temperature of air and substrate in both active and inactive lizards.