The karyotypes of two Turkish populations of Rana ridibunda were analyzed. In the two groups, chromosome numbers were identical (2n = 26), and general chromosome morphology was similar, although differences in the morphology of several chromosomes were found. In the Izmir population, chromosome 2 was metacentric and chromosome 3, submetacentric. The opposite was found in the Beysehir population. Chromosome 4 was metacentric in Izmir but morphologically variable in Beysehir. Almost half of the Beysehir samples had one metacentric and one submetacentric chromosome 4, a polymorphism that was shown to be correlated with the heteromorphic sex chromosomes in males. Out of the smaller pairs, chromosome 10 from Izmir and chromosome 9 from Beysehir were subtelocentric and were characterized by a secondary constriction on their long arm.