We incubated eggs of Calotes versicolor at four constant temperatures ranging from 24°C to 33°C to assess the effects of incubation temperature on hatching success, embryonic use of energy, and hatchling phenotypes that are likely to affect fitness. All viable eggs increased in mass throughout incubation due to absorption of water, and mass gain during incubation was dependent on initial egg mass and incubation temperature. The average duration of incubation at 24°C, 27°C, 30°C, and 33°C was 82.1 days, 60.5 days, 51.4 days, and 50.3 days, respectively. Incubation temperature affected hatching success, energy expenditure for embryonic development, and several hatchling traits examined, but it did not affect the sex ratio of hatchlings. Hatching success was lowest (3.4%) at 33°C, but a higher incidence of deformed embryos was recorded from eggs incubated at this temperature compared to eggs incubated at lower temperatures. Most of the deformed embryos died at the last stage of incubation. Energy expenditure for embryonic development was, however, higher in eggs incubated at 33°C than those similarly incubated at lower temperatures. A prolonged exposure of eggs of C. versicolor at 33°C appears to have an adverse and presumably lethal effect on embryonic development. Hatching success at 24°C was also low (43.3%), but hatchlings incubated at 24°C did not differ in any of the examined traits from those incubated at two intermediate temperatures (27°C and 30°C). Hatchlings incubated at 33°C were smaller (snout-vent length, SVL) than those incubated at lower incubation temperatures and had larger mass residuals (from the regression on SVL) as well as shorter head length, hindlimb length, tympanum diameter, and eye diameter relative to SVL. Hatchlings from 33°C had significantly lower scores on the first axis of a principal component analysis representing mainly SVL-free head size (length and width) and fore- and hindlimb lengths, but they had significantly higher scores on the second axis mainly representing SVL-free wet body mass. Variation in the level of fluctuating asymmetry in eye diameter associated with incubation temperatures was quite high, and it was clearly consistent with the prediction that environmental stress associated with the highest incubation temperatures might produce the highest level of asymmetry. Newly emerged hatchlings exhibited sexual dimorphism in head width, with male hatchlings having larger head width than females. J. Exp. Zool. 292:649–659, 2002. © 2002 Wiley-Liss, Inc.