The results of the 2002 census pointed out to an enormous increase in the number of inhabitants who were nationally undeclared or undecided. In the inter-census period 1991-2002, this population group increased for more than ten times (from 5 054 to 55 016). According to the share in the total population of Vojvodina (2.71%), they are - along with the Croats (2.78%) and the Slovaks (2.79%) - located immediately after the most numerous nationalities, the Serbs and the Hungarians. The paper analyzes the basic demographic characteristics (gender and age structure) of the undeclared and undecided persons, as well as the differences and similarities with other nationalities. The paper also presents the unequal spatial distribution of that population (at the settlement and municipal level), pointing out the interdependence between a great number of Yugoslavs and the enormous increase in the persons who were nationally undeclared or undecided. Using the features mother tongue and religion, the author tried to establish the relative relation between the number of the nationally undeclared and the number of nationally undecided persons.