Cognomen Istvanic (Istvanic 
) , throughout the world, is a very rare surname. The family name Istvanic is characteristic of Croatia, where it is a rare surname, Germany, where it is a very rare surname, and Canada, where it is an extremely rare surname. Measured by absolute frequency, it is the most numerous in Germany, Croatia, and the United States. Very seldom, Istvanic is the forename as well as the last name.