Development and survival of reptilian embryos are affected by the temperature and moisture within the nest. Moreover, thermal and hydric conditions during incubation also affect phenotypes of hatchlings. Thus, females should select nest sites that enhance hatching success and produce hatchlings with phenotypes fit for the local environment. The objective of this study was to determine the substrate temperature and moisture conditions selected by eastern fence lizards (Sceloporus undulatus) for nesting. In the laboratory, gravid females were housed in a large enclosure that provided suitable nesting substrate. Gradients of temperature and moisture within the substrate were established to provide a wide range of conditions from which females could choose. Fifteen (65%) females selected nest conditions within the moisture and temperature range that results in successful embryonic development. Two females (9%) nested in extremely dry conditions, and six females (26%) oviposited on the substrate surface. Females that nested in the field selected nest sites with similar conditions as females that nested in the laboratory. In general, we provide support for the idea that females choose nest sites with thermal and hydric conditions that are associated with positive hatching success.