The dietary breadth of the western diamond-backed rattlesnake (Crotalus atrox) has been well documented; however, the relationship of species of prey and optimum energetic intake (e.g., size) is poorly understood. While lagomorphs have been documented as prey, their regularity in diets of C. atrox has not been examined. During several studies of C. atrox in Arizona, we collected dietary data through direct and indirect observation and analysis of scat. Lagomorphs were regularly included in the diet of adult C. atrox at all sites. Our observations suggest that C. atrox might select prey based on size to benefit from maximum energetic intake per feeding event.