The subject of this paper is the relationship between the stability of synthetic case system and noun categories in sirinić speech, which is a part of prizren-timoc dialect zone in Serbian language. The existing foundings about synthetic declensions and categories of gender and number have been tested by using corpus and quantitative method in this paper. This research has confirmed that synthetic cases are better preserved in singular than in plural and that they are the most stable in feminine nouns, less in muscular and the least stable in neuter nouns. In plural, dative remains only in musculine and femine nouns. A greater number of cases has been found in singular, but their percentage compared to general case indicates that they persisted only in limited functions and meanings.