The material consisted of 300 skulls (150 male and 150 female) of adult European bison from the Lowland line aged 5 to 27 years. The specimens belong to the museum collection of the Mammal Research Institute of the Polish Academy of Sciences in Białowieża. On each skull three standard measurements (BP, EctEct, SmSm) were taken. The results were standardized separately for males and females. The sum of three normalized parameters describing each skull was treated as its standardised dimension and then Perkal's natural similarity coefficients were calculated. In adult males a remarkable polarization of skull shapes was observed. In one set of the male specimens the type of a long skull with a broad forehead and narrow face was predominant (27%). In another, opposite and almost equally numerous (24%) set of male specimens, the type of a short skull with a narrow forehead and broad face prevailed. Such a polarization was not found in adult females: the type of a long skull with a narrow forehead and narrow face dominated (28% of the examined material); the remaining variants were evenly distributed.