Astacus leptodactylus is one of the four native species from Astacidae family in Croatia, and it is a keystone species in freshwater ecosystems. Data on this species on the European level is generally missing. The main goal of this graduate thesis was to investigate the morphometric characteristics of this species and to analyse differences in morphometry among 4 populations from the following sites in the north-west Croatia: Mrežnica, Treće Maksimirsko Lake, 1st and 2nd part of the Rakitje Lake. The goal was to compare the results of the morphometric analyses with the previously obtained molecular analyses results. It has been established that there are statistically significant differences among the examined populations of males and females in measured morphometric characteristics. These results confirmed the molecular - phylogenetic studies, this species shows intraspecific divergence among different populations. The results of discriminatory analysis have shown that differences in morphometric characteristics between populations reflect geographical distance. The observed differences in morphometric characteristics between populations of narrow-clawed crayfish are most likely the result of the combination of genetic and environmental mechanisms. This thesis has confirmed that morphometric analyses, combined with statistical methods, are useful in differentiating and separating crayfish populations. The obtained results will be useful in all further research of A. leptodactylus, both in Croatia and in Europe.