© Inter-Research 2012. This study provides the most comprehensive evaluation to date of the temperature range that produces mixed sex ratios as well as the temperature that produces a 1:1 sex ratio (denoted 1:1 temperature in the following) in the Kemp's ridley sea turtle Lepidochelys kempii. We analyzed temperature data from Padre Island National Seashore (PAIS), Texas (USA). Using 2006 to 2008 PAIS sex ratio data sorted by mean temperature, which fluctuated minimally in this study, we found a 1:1 temperature of 30.0°C utilizing the Hill distribution model. The upper limit of the temperature range that was estimated to produce mixed sex ratios was 32.5°C; the lower end could not be determined. These values are in the upper range of those reported for other sea turtle species, except the olive ridley. The Kemp's ridley temperature-dependent sex determination parameters described here can be used to predict sex ratios from nests with known incubation temperatures in order to help manage the recovery of this species.