While still an amateur player, Forson became a member of the Togo national team. His national debut came in May 2001 in a 1–0 victory against Senegal. His revelation was in a four countries tournament in Iran (Paraguay, Macedonia, Iran and Togo). He was called up to the squad to participate in the 2006 World Cup where he started in two games vs France and Switzerland. Both games resulted in 2–0 losses though Forson played strongly in the game vs France, effectively marking and containing French notable players such as Thierry Henry, Ribéry, Govou and Malouda.