Sex in many reptiles is determined by temperature during development (temperature-dependent sex determination; TSD) rather than by an individual's genotype (genotypic sex determination; GSD). TSD has numerous ecological and evolutionary implications, and whether or not species display TSD is of conservation concern because substantial habitat and climate change have the potential to skew sex ratios. It is therefore important to describe the means by which sex is determined in reptile species. To date, the sex determination mechanism is not known for any species within the Anguidae, a diverse lizard family that is globally distributed. I used controlled incubation experiments to test the hypothesis that Southern Alligator Lizards (Elgaria multicarinata) display TSD. Offspring sex was assessed by direct examination of the gonads after incubation in one of five constant-temperature treatments (24°, 26°, 28°, 30°, and 32°C). Developmental temperature did not affect offspring sex, indicating that E. multicarinata does not display a strict form of TSD. Rather, my results indicate that E. multicarinata displays GSD, as is most common in vertebrates, although I cannot rule out the possibility that sex determination is somewhat thermally sensitive. Further work with additional samples and other anguid species is clearly needed.