Аннотация:This is the first record of specific morphological deviations in the marsh frog on the territory of Russia. Similar anomalies were discovered by Jean Rostand in the 1950s in France and named by him as the “anomaly P”. Our observations were made on the territory of the Privolzhskaya Lesostep’ Nature Reserve (Penza region, Central Russia) in 2016 and 2017. The anomaly P was found in 17.6 % of individuals. Mild forms of the anomaly P (polydactyly and polyphalangy on the hind and fore limbs) were registered in 11.4 % of individuals, whereas severe forms of the anomaly P were found in 6.2 % of all individuals. The potential causes of the anomaly P are discussed.