He has been summoned for questioning and can be held for up to 48 hours without being charged as part of a police probe into the organisation of sex parties in restaurants and swingers' clubs in Paris, Washington, Madrid, Vienna and Ghent, Belgium.
Magistrates have already charged several leading figures from Lille with organising the ring said to have operated out of luxury hotels in the city. There are suspicions that a construction company executive used his firm's money to entertain guests at sex parties.
DSK, as he is known in France, could face charges if magistrates deem he was aware the women who took part were prostitutes and the funds to pay them were fraudulently obtained, as is being alleged against other suspects.
Strauss-Kahn, 62, resigned as director of the International Monetary Fund in May after he was accused of raping a chambermaid in a New York hotel Nafissatou Diallo. He returned to France in August after the US case collapsed, only to face new allegations.
First, a 32-year-old writer accused him of attempting to rape her in 2003 but, while prosecutors said there was prima facie evidence of sexual assault, the case was too old to pursue.
Then he was implicated in the entirely separate investigation into the alleged prostitution ring.
The press has also carried reports of Strauss-Kahn attending parties in a Paris hotel with Lille's chief of police and the alleged kingpin of the ring 'Dodo la Saumure', who runs massage parlours in Belgium.
He had asked to be questioned by judges leading the inquiry, hoping to halt what his lawyers called a "media lynching."
Once seen as the favourite to oust Nicolas Sarkozy and win April's French presidential election, Strauss-Kahn is now an embarrassment to his Socialist Party, shunned by the campaign and former close allies.
He still faces a civil suit from the Diallo.