Osteological investigations of the Rivers Sava and Danube sampling of the bighead gobyNeogobius kessleriskull, pectoral girdle, and gill cover (50 characters) revealed values for some descriptive statistics parameters different from those obtained for the Dnjepar estuary population. Sexual dimorphism was not detected for any character. Certain characters of skull, suboperculum, praemaxilla, and hyomandibular were significantly different in particular length classes. Allometry was not detected. Multivariate analysis revealed that morphology of the biggest specimens is rather different from that of smaller ones. Overall, the results were consistent with a direct morphological formation through the bighead goby ontogeny. It was suggested that great variability in size classes, especially in the largest one, weakens their clear separation, and that the size component has a strong influence on the head skeleton shape.