There is no one, official, united Hungarian Orthodox Church. Many Orthodox churches are present in the country or lay claim to some territory of the former Austro-Hungarian Empire, but most Byzantine or Eastern Christians of the modern, sovereign nation of Hungary belong to the Byzantine Catholics, united with the Pope of the Roman Catholic Church.
Over 50% of the population of Hungary is Roman Catholic. Another 20% is Calvinist. The largest minority faith group is the Lutherans. Greek or Byzantine Catholics and Eastern Orthodox do not make up a significant percentage of the demographic.
The Kingdom of Hungary, or "Realm of the Crown of St. Stephen", encompassed a very different area than the modern nation of Hungary. In one sense, one could speak of the Patriarchate of Karlowitz (Sremski Karlovci), later integrated into the Serbian Orthodox Church, as the only "Hungarian Orthodox Church" in history. The Sremski Karlovci, formed in 1765, was comprised of all the Orthodox Serbs found in the Kingdom of Hungary, and consisted of six suffragan sees on Hungarian territory.
Other "Hungarian Orthodox", or Eastern Orthodox Christians of the territories of the former Kingdom of Hungary, now find themselves on Romanian, Slovak, Czech, Croatian and Bosnian territory and belong either to the Church of Serbia, the Church of Romania, or the Church of the Czech Lands and Slovakia.
- John Meyendorff, The Orthodox Church, Crestwood, NY, 1996, p. 146.