We estimated differences in body size and age structure of two populations of Pelophylax ridibundus living at different altitudes in Turkey, one from Dörtyol (6 m a.s.l.) and the other from Karagöl (1480 m a.s.l.). Their age structure was determined by skeletochronology performed on the LAGs (lines of arrested growth) of the phalanges. While ages ranged from 2 to 8 years for males and from 2 to 7 years for females in Karagöl, in Dörtyol the ages ranged from 4 to 11 years for males, and 3 to 7 years for females. Sexual size dimorphism was only found in the Dörtyol population. Larger females tend to be found in hotter climates (Dörtyol) but reach maturity later (3-4 years) than the highland population (2 years). A significant relationship between age and snout-vent length (SVL) was found for both sexes and populations with the exception of females in Dörtyol.