The Jacky Dragon Amphibolurus muricatus (White, ex Shaw) is a widespread and abundant species in eastern Australia. Its range overlaps some of the more heavily populated urban areas of Australia where natural habitat is being rapidly lost and/or fragmented. We collected Jacky Dragons over four years in extremely fragmented native remnant vegetation at the edge of an urban golf course in Sydney. The size structure of the population remained similar over the study period. However, there was a lack of large individuals, both male and female. The sex ratio of adult males and females was equivalent rather than conform to the expectation that there would be more females than males in this temperature-dependent sex determined species. Increased sexual aggression and loss during migration were the most likely causes for the loss of larger individuals and for the loss of female bias. These imbalances are predicted to threaten the longer term viability of this urban reptile population.