Personal names are an important part of human identity and a subject of onomastic study. In the introduction of this master paper development, structure, origin and grammatical categories of Croatian proper names regarding contemporary Croatian names fund are presented and also grammatical categories and declension types of Croatian and foreign proper names. Speakers of Croatian language often have difficulties in determining declension types and case forms of Croatian and foreign proper names. These difficulties occur on the level of spelling and morphology, i.g. morphonology regarding: (non) hyphenated double names, (non) implementation of sound changes, (non-)insertion of the intervocalic j, declension of female foreign names in zero/null morpheme, declension of male foreign names etc. Solutions in normative manuals are very often not systematic and inconsistent. The aim of this master paper was to present preferred solutions in the instances of normatively permitted doubles (or the absence of a prescribed rule), as well as into the degree of students’ mastery over normative rules or deviation from the norm in the cases where there is only one correct solution. The analysis of the results in a questionnaire that consisted of 35 questions, and has been conducted among 40 students of prevalently philological orientation at the University of Zadar, has confirmed that the relation between norm and usage is very complex and it is hard to presuppose which form will prevail in use. Deviation from the norm occurs also in examples for which the solutions in normative manuals are systematic and clear.