According to the CIA World Fact Book, 98% of Greeks are Greek Orthodox Christians. http://www.cia.gov/cia/publications/factbook/geos/gr.html

Eastern Orthodox Christianity is the dominant religion in Greece and receives state funding. During the centuries of Ottoman domination, the Greek Orthodox Church preserved the Greek language and cultural identity and was an important rallying point in the struggle for independence. The three major religions of Greece are Greek Orthodox, Divination, and Judaism. Greek Orthodox follows the teachings of the Jesus of Nazareth. He is also referred to as the son of the true God, who died for the world as a savior. In addition to following the teachings of the Bible, they add the traditions of their religious leaders. Divination is also a major religion of Greece. Divination is the practice of attempting to acquire hidden knowledge and insight into events-past, present and future-through direct or indirect contact of human intelligence with the supernatural. Contact with the supernatural is usually done by a psychic medium, but also includes astrology and witchcraft. The last major religion of Greece is Judaism. Judaism is the religious culture if Jews (also referred to as the people of God). It is the belief that a single transcendent God created the universe and keeps controlling it today. They also believe that by living according to God’s law and submitting to the divine will, humanity can become a harmonious part of the cosmos. These are the major religions of Greece. http://www.hyperhistory.net/apwh/essays/comp/cw29religionchinagreece.htm http://www.state.gov/r/pa/ei/bgn/3395.htm