Playboy's Bad Girls Karissa and Kristina Shannon

In 2008, Hugh Hefner of Playboy chose the Shannons to be two of his three new girlfriends, replacing the departed Bridget Marquardt and Kendra Wilkinson. (Crystal Harris replaced Holly Madison as Hefner's "number one" girlfriend with whom he shares a bed.) Because of their relationship with Hefner, the Shannons have appeared on E! network television series The Girls Next Door. Despite the girlfriend status, Karissa claims the relationship she and Kristina shared with Hugh Hefner was more for fun and the opportunity to be on the show, rather than romance.

On January 14, 2010, Hugh Hefner revealed that the Shannons were moving out of the mansion to the local Playmate house with his blessing. They will continue to appear in The Girls Next Door.

The Shannons appeared as Miss July and Miss August 2009 in the double "summer issue" of Playboy that incorporated July and August in a single edition. Although they shared a single centerfold, they are the only twins to be designated Playmate of the Month for two distinct months. This was the first time since March 1955 that the magazine did not publish an issue for each month of the year; according to London's Daily Telegraph newspaper, this was due to significant losses in the company's value (down from $1 billion in 2000 to $84 million in 2009).