Sexual dimorphism and reproductive cycle were studied in a population of Sceloporus horridus horridus from a tropical dry forest in central Mexico. Males with 90.66 mm (71.5-111.0 mm ± 12.79 mm) snouth vent-length were larger than 86.32 mm (71.0-101.0 ± 7.94) females. Reproductive activity is seasonal in both sexes and occurs in the period spring-summer as it has been observed in several oviparous species of tropical dry forest. The vitellogenesis occurs between March and April and the spermatogenesis from February to March. The ovulation occurs on late April and the eggs are in the oviducts between May-July. Mean eggs mass was 0.46 g (0.3-0.6) and meanclutch size was 15.3 eggs (10-20). Clutch size was related significantly to mass (r = 0.669) and physical condition of females (r = 0.676). The relative clutch mass value was 0.31 conforming to the strategies predicted for sit and wait species of lizards. The on set of reproductive activity in males was related with temperature (r = 0.508) and in females with precipitation (r = 0.775). Liver and fat body mass in males and females, showed an inverse relationship with the peaks of breeding activity.
