Morphological characteristics of island populations of the sleepy lizard, Trachydosaurus rugosus, were compared with those of three adjacent mainland populations in South Australia. An analysis of 21 morphological characters revealed greater divergence among the island populations than among those on the mainland. However, in contrast with the findings of an earlier study using allozyme electrophoresis, morphological relationships among populations showed little congruence with the relationships expected from their geographic proximity. Two measures of developmental stability (fluctuating asymmetry and percentage gross abnormalities) varied significantly among the populations. High levels of developmental instability were observed in three of the island populations. It is not possible to rule out environmental causes of the increased developmental instability but it appears more likely that it is caused by genetic drift and inbreeding resulting from small population size. These results suggest that developmental stability may be more useful in monitoring genetic changes in wildlife populations than the conventional method of allozyme electrophoresis.