We studied reproduction and sexual dimorphism of Aspidoscelis gularis from an arid environment in Guadalcázar, San Luis Potosí, Mexico. Males reached sexual maturity at a larger snout-vent length (55. 2 mm) than females (52. 4 mm). Males and females were similar in size, but males had larger heads and longer hindlimbs than females. Reproductive activity of both sexes was synchronous, similar to other species of the genus Aspidoscelis. Testicular recrudescence occurred February–March and maximum activity was March–October, and regression was in November. Vitellogenesis occurred February–September, with ovulation and fertilization occurring in June. Mean size of clutch of oviductal eggs was 3.0 ± 0.32. Size of clutch was not related to snout-vent length. Proximal factors influenced timing and intensity of reproduction in A. gularis.