The whiptail lizard Cnemidophorus vanzoi is a large-bodied teiid found only on two islands (Maria Major and Maria Minor), off St Lucia, West Indies. In May 1995, 42 lizards from Maria Major were introduced to the smaller uninhabited Praslin Island on the same coastline. Three years post-release, we studied abundance, demography and morphometrics of the translocated lizard population, during a 6-month period covering wet and dry seasons. Age, sex, snout–vent length (SVL), body mass (BM), tail length, tail regeneration, and overall condition (moulting, reproductive condition, cuts, external parasites) of 107 animals caught during the study are analysed in the present paper. Comparisons are also made with the source population. A body condition index (CI (BM/SVL)), sex ratio (adult males : adult females), age ratio (adults : juveniles), and sexual size dimorphism ratio (SVL adult male : SVL adult females) were calculated for the study population. Distance sampling and mark–re-sight surveys were used to estimate population size and lizard density. A total of 155 ± 26 individuals were estimated. The lizard population was found to have a high growth rate (r = 0.97–3.95). There were significant seasonal changes in lizard abundance. Seasonal differences in lizard numbers, BM and CI suggest either severe resource limitation during the dry season, or selective aestivation. A high frequency of tail autotomy may point to intense intraspecific competition as the island is relatively free from main predators such as the black rat Rattus rattus. Sex ratio, sexual size dimorphism and sexual dichromatism all indicate a territorial species in a generally non-territorial family (Teiidae). Some adult males seem to maintain juvenile colours. It is suggested that the introduced population has successfully colonized its new environment and that no significant change in the animals condition or size has occurred during the 3 years since translocation.