Sexual dimorphism in the genus Sceloporus has historically been relatively well studied; however, there is little understanding of how patterns of sexual size dimorphism might vary within species and how that might affect our ability to generalize about the evolution of sexual size-dimorphism in Sceloporus and other organisms. We examined sexual size-dimorphism in a population of Sceloporus spinosus from Guadalcázar, San Luis Potosí, Mexico. Males (n = 85) and females (n = 63) showed no significant sexual dimorphism in size of the body, head, or legs. In combination with the results of other studies on sexual dimorphism in S. spinosus and closely related species of Sceloporus, our results suggest that there can be variation in sexual size-dimorphism within and among species that can limit the ability to make broad generalizations about the phylogenetic patterns of sexual dimorphism in Sceloporus.