To understand the effects of island and mainland on life history traits (e. g. longevity, age at maturity, body size and body mass) of the smooth newt Lissotriton vulgaris (Linnaeus, 1758), we generated data on age and body measurements for an island (Bozcaada) and a mainland (Canakkale) population in northwestern Turkey. Age was determinated by skeletochronology. The maximum life span was 4 years in the island population and 5 years in the mainland population. Age at maturity was estimated to be 2-3 years for both sexes and the populations. While mean snout-venth length (SVL) was calculated as 35.56 mm for females and 31.95 mm for males in the mainland population, it was found to be 32.83 mm for females and 31.78 mm for males in the island population. Females from the mainland population were found to be significantly larger and heavier than those of the island population. A significant positive correlation was found between SVL and age for only males in the mainland population. Unexpectedly, age was not correlated with body size for the island individuals. Since there were hardly any demographic studies on any Urodela species comparing island and mainland populations, in this paper we contribute to the literature on this subject.