The brown marmorated stink bug is a new invasive species of the stink bug family (Pentatomidae) in Europe. It is a polyphagous pest that attacks more than 200 plant species, and economic damage to the cultivation of fruits, vegetables, and field crops has been observed. Since the species has been present in Croatia only for a short time, little is known about its biology and ecology, but also about its morphological variability. The aim of the work is to determine the morphological variability of the population of this pest using the methods of geometric morphometrics and to compare the variability of the population from Croatia with the variability of the population of the pest from Slovenia and Serbia. Samples of brown marmorated stink bug were collected in agroecological systems of Croatia, Slovenia and Serbia in the period from 2018 to 2021. A total of 545 stink bugs were collected, from which the upper and lower wing pairs were removed and prepared according to the standard procedure. To determine morphological variability, specific points were placed on the wings (a total of 12 points on the upper wings and 16 points on the lower wings), and multivariate statistical analysis was used in the analysis of the shape and size of the wings (principal component analysis (PCA) and canonical discriminant analysis (CVA)). The results of the study showed significant differences in the shape of the wings between the pest populations from Croatia, Slovenia and Serbia, suggesting a gradual adaptation, i.e. acclimation of the species to the new area to which it has recently migrated. Sexual dimorphism of the species was not detected, but minimal differences in forewing and hindwing shape were found between males and females of the brown marmorated stink bug from different countries.