We determined annual survivorship and causes of mortality at two Desert Tortoise, Gopherus agassizii, study sites in the Sonoran Desert, Arizona, based on radio-telemetry data. Annual survivorship was high (89–97%), did not differ between sexes, and was comparable to previous studies using mark–recapture methods. Survivorship between sexes differed seasonally at one site, based on differences in seasonal activity patterns and differential exposure to predation by mountain lions, Puma concolor. In the absence of mammalian predation, seasonal survivorship did not differ between sexes. The next leading cause of mortality was failure to right oneself after a fall or after being flipped during reproductive or combat events.