Incubation temperatures in loggerhead sea turtle (Caretta caretta) nests were examined as a method for predicting hatchling sex ratios. Incubation temperatures were recorded in 40 nests that were laid on Hutchinson Island, Florida. Small temperature data loggers were placed directly in nests (in the center of the egg mass) and were programmed to record temperature every 1.2 h for the entire incubation period. Nests laid during the early, middle, and late portions of the peak nesting period (June and July) were examined. The nests were equally distributed on an untreated beach and a beach that had been artificially supplemented with sand to compensate for erosion. Three nests received multiple data loggers to assess temperature variation within the nest. The average daily temperatures within these nests varied from a maximum of 2.1°C at the top of the egg chamber to a minimum of 0.4°C at the bottom. During the thermosensitive period, temperatures in the center of the egg mass were significantly higher than those at the top and bottom of the egg chamber (average difference was 0.4 and 0.9°C, respectively). Incubation temperatures within all 40 nests were relatively high, suggesting an overall sex ratio that is highly female biased. Using nest temperature during the thermosensitive period as a predictor, the hatchlings from 37 of the 40 nests were predicted to be 100% female (i.e., 92.5% of the nests). The other three nests had been laid adjacent to or in contact with the vegetation bordering the beach and were shaded by the vegetation during the afternoon. Two of these nests were predicted to produce female-biased sex ratios and one was predicted to produce a sex ratio of nearly 1:1. For beaches examined, the sex ratios were highly female-biased; however, nest temperatures on the beach supplemented with sand were significantly higher than those on the untreated beach. The highly biased sex ratio predicted for Hutchinson Island is similar to that estimated for another C. caretta nesting beach located at Cape Canaveral, Florida. These data collectively suggest that C. caretta nesting along the Atlantic coast of Florida consistently produce hatchlings whose sex ratios are distinctly female-biased.