The club, which Aftonbladet compared to that in the Brad Pitt film Fight Club, is said to meet on a fishing boat moored on Söder Mälarstrand in Södermalm, central Stockholm.
The paper said that combatants, who are usually amateurs, fight until one of them is “lying lifeless and bloody on the ground.”
Sweden has long enforced a ban on professional boxing, but police sources said that privately arranged bare-knuckle boxing events are entirely legal.
“To fight with someone who is willing is not a crime,” commissioner Ali Lindholm of Stockholm police told the paper.
The combatants and spectators are said to include well-known figures from the Swedish film industry, as well as estate agents, salesmen and a number of people well-known in the upper-market bars and clubs of Stockholm’s Stureplan area.