Mary-Kate Olsen has entered a clinic for treatment of an eating disorder, People magazine is reporting on its Web site, www.people.com.

"Mary-Kate Olsen recently entered a treatment facility to seek professional help for a health-related issue," Michael Pagnotta, a spokesman for Mary-Kate and Ashley Olsen, who turned 18 on June 13, said in a statement Tuesday. He did not specify what that health issue was.

Pagnotta added: "She is thankful for the encouragement and support of her friends and family who are with her every step of the way."

The sisters, who each boast an estimated net worth of $150 million and will enter New York University as freshmen in September, commented on gossip in a People cover story last month. "Being in the public eye, you're labeled that you have an eating disorder," said Ashley. "You have a drug addiction," said Mary-Kate.

Ashley, however, was quick to add: "We don't have problems! There's nothing to worry about."

Insisted Mary-Kate: "If I had a drug addiction, I would be in a thingy - like Promises, the Malibu (rehab) place. You don't see me there. So, like, come on. It's crazy."