Simao calls time on Portugal career
"After a long period of reflection, I believe the time has come to bring an end to my international career and create room for new players," said the 30-year-old, who won 85 caps for Portugal and scored 22 international goals.
In a letter made public by the Portuguese Football Federation (FPF), he said he was retiring for "personal reasons".
Simao began his professional career at Sporting Lisbon, the same place as his compatriots and fellow wingers Luis Figo and Cristiano Ronaldo.
He spent two years at Barcelona between 1999 and 2001 before returning to Lisbon and joining Benfica, who he captained to victory in the league and the Portuguese Cup.
He joined Atletico in 2007 and last season won the inaugural Europa League with the side from the Spanish capital.
The bustling, right-footed player was a member of the Portugal team that won the Under-16 European Championship in 1996 and he was also in the senior squad that finished runners-up to Greece on home soil at Euro 2004.
He played four times at the recent 2010 FIFA World Cup™ in South Africa, scoring in the 7-0 thrashing of Korea DPR in the group phase.
"I regret his decision, but naturally I have to accept it," said FPF president Gilberto Madail in a statement.
"For his huge talent and for that huge desire to represent his country in the best way possible, Simao remains and will always remain a symbol of the national team."