We used capture-recapture techniques and skeletochronological analysis to investigate body size, population size, and age structure of a population of Palmate Newts (Lissotriton helveticus) living in two adjacent lakes at 2,300 m in Andorra (Eastern Pyrenees). Females were larger (minimum–maximum, 31.0–47.0 mm vs. 32.0–42.0 mm) and heavier (0.8–2.1 g vs. 0.5–1.8 g) than males. The total adult population of the two lakes is estimated at 338–245 individuals. Both sexes mature in three years; males live for nine years and females up to eight years. Interpopulational differences in demographic traits between this population and low-altitude populations of L. helveticus do not include the predicted pattern of delayed sexual maturity and larger longevity that would be expected to exist in higher altitude populations.