We studied the ecology of a population of the mountain knob-scaled lizard, Xenosaurus grandis agrenon, from Oaxaca, México. Males and females did not differ in body size (SVL), but males did have larger heads and hind limbs than females. Mean litter size was 3.2. Sex ratio did not differ from 1:1. All lizards were found associated with crevices. The size of the crevice (thickness and depth) increased with lizard SVL. Mean body temperature was 25.6°C. Body temperature was related to air and substrate temperature. Body temperature was influenced by the amount of cover, and the lizard's body position in its crevice but not by sex, month, vegetation type, or any crevice characteristics. We compare the ecology of this population to that of other Xenosaurus.