Muntari's abilities first came to light in youth tournaments, while he was playing for Liberty Professionals youth team. He became a regular member of Ghana U20 team at the age of 16 as they finished runners-up at the 2001 FIFA World Youth Championship in Argentina, losing out to the hosts in the final. Despite impressing during a trial with Manchester United after the tournament, he ended up joining Italian club Udinese.
He won his first senior cap against Slovenia on 17 May 2002, and became a regular fixture in the team as The Black Starsopened their 2006 FIFA World Cup qualifying campaign. He was selected for the Olympic side at Athens 2004, but was sent home for disciplinary reasons. This started a dispute between Muntari and his federation, and he said that he would refuse to play for his country again, beating the record for the youngest international retirement. He retracted, making a public apology to the federation, and was selected for the 2006 World Cup squad. He played in the first two matches, a 2–0 defeat by Italyand a 2–0 win over the Czech Republic, in which he scored, but having received a yellow cards in each game, he was suspended for the game against the United States, but returned for the second round match against Brazil, in which Ghana was eliminated.