Hollywood stars are very well-known for getting a little nip here and a little tuck there. In fact, L.A. plastic surgeons are so good these days that we're often left wondering — well, did they or didn't they? However, some celebs are just plain hard to recognize from how they looked years ago. They've been completely transformed!
Think you've seen it all in the celebrity world? Think again! Here are 13 stars you might not recognize after their plastic surgery. Happy guessing!
Who do you think looks most different?
Image via Dara Kushner/INFphoto.com/Splash News
Uma Thurman: Before

Here's Uma in 2011. Nothing out of the ordinary, right?
Uma Thurman: After

When Uma Thurman appeared at the premiere for the miniseries The Slap, people went, "Huh?" She looked so different!
Pamela Anderson: Before

Baywatch babe Pamela Anderson has always been the fantasy of men across the world.
Pamela Anderson: After

But, though still gorgeous, her hair isn't the only thing that's different about her these days.
Renée Zellweger: Before

In 2009, Renée Zellweger looked pretty much the same as she did in her Jerry Maguire days.
Renée Zellweger: After

However, the actress surprised many with her new look recently. It barely looks like her!
Tori Amos: Before

If you were an angst-ridden teenage girl in the '90s, you had this Tori Amos album.
Tori Amos: After

However, you might be surprised to see that this is what Ms. Amos looks like now. Forever a goddess, though!
Jennifer Grey: Before

Part of Jennifer Grey's charm in Dirty Dancing was her gorgeous and unique nose, but apparently, she didn't like it.
Jennifer Grey: After

Grey has admitted that she regrets the nose job that made her look like a totally different person. "I went in the operating theater a celebrity — and came out anonymous," she said. "I'll always be this once-famous actress nobody recognizes … because of a nose job."
Kylie Jenner: Before

Kylie Jenner has always been gorgeous, but here's what she used to look like. 'Memba this?
Kylie Jenner: After

Kylie looks much different now than she did a few years ago. She's admit to using "temporary lip fillers," but is that all she's done? Hmmm …
Meg Ryan: Before

In 1998, here's what Meg Ryan looked like — soooo '90s!
Meg Ryan: After

Ten years later, the actress had a much different look.
Melanie Griffith: Before

Melanie Griffith was fresh-faced (and thin-lipped) back in the '80s.
Melanie Griffith: After

Melanie is still gorgeous, but it's almost hard to believe this is the same person!
Courteney Cox: Before

Courteney Cox has always been insanely gorgeous, but she looks a little bit different here from how she looks …
Courteney Cox: After

Here! It's difficult to pinpoint what the Cougar Town actress has had done exactly, but it's hard to believe nothing!
Jennifer Aniston: Before

When Jennifer Aniston starred in Leprechaun in 1993, her nose looked mighty different.
Jennifer Aniston: After

There's no denying that the stunning A-lister looks slightly different now. Always gorgeous, though!
Demi Moore: Before

When Demi Moore was married to Bruce Willis, here's what she looked like. Cute!
Demi Moore: After

Wow! Demi looks sooo different now — and it isn't just the hair!
Madonna: Before

Old-school Madge. Cool as hell, but a far cry from how she looks now.
Madonna: After

Madonna at the Met Gala a few weeks ago. Aging gracefully?
Robin Wright: Before

Here's Robin Wright with then-husband Sean Penn in 2003.
Robin Wright: After

Annnnnd here's Robin Wright now. Good genes or good docs?