The incredibly shrinking Ali Lohan?

Months after she shot down rumors that she underwent plastic surgery, Lindsay Lohan's 17-year-old sister showed off an equally troubling transformation heading to a model casting in Beverly Hills on Tuesday.

Climbing out of a white SUV, the budding catwalker, clad in tight jeans, boots and a tucked-in white shirt, appeared alarmingly gaunt and pale -- with noticeably stick-thin arms and legs.

Lohan (who now asks to be called by her full name, Aliana) recently told Page Six Magazine that she was "cracking up" over rampant speculation that she had numerous plastic surgery procedures to alter her face.

"Because, like, when would I do that (surgery)? I'm 17 years old. That's not legal! I would need my mother's signature, and do you think my mom would sign off on that? No! It's not the right thing to do," said the young star, who recently signed with Next Model Management.

Ali's older sister Lindsay, 25, famously had a scary-skinny phase, too -- debuting a gaunt, thin body in early 2009.

Tell Us: Does Ali look too thin?