Mary-Kate Olsen
Photo: Amy Sussman/ Getty Images

Mary-Kate Olsen has been hospitalized for a kidney infection, her rep confirmed to MTV News.

The actress, who turned 21 this year, sought emergency-room treatment in a New York hospital for the infection on Monday and is expected to make a full recovery.

"She is resting comfortably and will be released in the next day or so," the actress' spokesperson said.

Olsen most recently guest-starred as Tara, a pot-smoking born-again Christian, on the Showtime series "Weeds," which aired its season-three finale on Monday. The "Full House" alum will appear on the big screen next year alongside Ben Kingsley, Famke Janssen, Josh Peck and Method Man in "The Wackness."

Olsen previously sought treatment for anorexia nervosa in 2004, when she checked herself into a rehab center in Utah (see "Mary-Kate Olsen Seeks Treatment For Eating Disorder"). She originally signed up for a month-long treatment, but extended her stay two additional weeks after making progress. Medical experts estimated she'd be fighting the disease for at least four to seven years (see "Experts Say Mary-Kate Olsen Faces Long Road To Recovery").

• Mary-Kate Olsen

Mary-Kate and Ashley Olsen (file)
Photo: Paul Hawthorne

While they may be media moguls with a combined net worth of around $300 million, Mary-Kate and Ashley Olsen are not above getting coffee for the boss. As part of their requirements at New York University's Gallatin School of Individualized Study, the twins have scored some sweet internships as first-year students.

Mary-Kate is working for A-list celebrity photographer Annie Leibovitz. Leibovitz, regularly published in the glossy pages of Vanity Fair, photographed the sisters as part of an advertising campaign for A&E's "Biography" last year. Mary-Kate's responsibilities are not likely to include handling film or anything potentially disastrous, but rather running errands, filing and other basic chores.

"They're having a chance to explore things that interest them that they never had a chance to do. It's an opportunity for both of them to learn from the best," said their rep.

A source close to the twins confirmed rumors that Ashley is interning with designer Zac Posen. She's probably not sketching out dress designs or cutting patterns, but, like Mary-Kate, is likely doing more standard gofer work — though she is no stranger to the design world. Seated in the front row at some of the top fashion shows, Ashley and her sister already tried their hands at designing, having launched their own line — aptly named mary-kateandashley — in 2001.

While they are earning credits, the NYU program promotes internships. The Gallatin School for Individualized Study's Web site explains the school's focus on practical experience: "The work may relate to the student's intellectual or creative goals or may be based on learning experiences related to the student's professional and career aspirations." Just in time, too. The twins have recently taken over management of Dualstar Entertainment, the company behind their $1 billion business empire. They have been co-presidents of the company since turning 18 last year.

• Mary-Kate & Ashley Olsen
• Mary-Kate Olsen