This number is changing every day, says head of operations Anders Kassman to Svenska Dagbladet.
His agency is keeping track of the 40 or so fighters who have returned to Sweden.
"We have a growing problem that we have to deal with in a sensible way and not spark panic," he says to Svenska Dagbladet.
Säpo, the Intelligence Service, does not want to say what crimes former IS fighters would be suspected of. Säpo has not identified anyone planning to make an attack in Sweden.
Since a terrorist blew himself up in a failed suicide bombing in 2010 on a crowded Stockholm street during the Christmas shopping rush, Sweden's Säpo have focused on preventing any more attacks. A third of their budget now goes to anti-terrorism, reports Svenska Dagbladet.