10. The Descent (2005)
What: One year after a bloody accident, six thrill-seeking women gather for a caving expedition in the Appalachians. But as their trip takes a turn towards disaster, the group soon realizes they’re not alone under the Earth.
Why: Just being alone in a cave is pretty damn scary — throw in a couple of bloodthirsty monsters after a group of untrusting adventurers and you’ve got a collection of terrorizing scares. Plus Director Neil Marshall doesn’t rest on his Crawler creatures to deliver the scares, the real meat of this horror flick is hiding in panic attacks, cave ins and in dirty secrets. The mutant creatures waiting to feast on your innards are just a bonus (and an excuse for some of the characters to do some mighty bad things).
Scariest Scene: The first time the group encounters a crawler, you only get a glimpse on the night vision camera, but poor Holly is the first to go.

9. The Ring (2002)
What: Based on Koji Suzuki’s novel Ring, this American adaptation of the 1998 Japanese film made many folks afraid of their TVs. As the movie legend has it, there’s this VHS tape that has a collection of discomforting black-and-white images. After you watch the video, your phone rings and a voice tells you that you’re going to die in seven days, leaving behind a twisted green corpse. The main character stumbles upon this tape and sets out to uncover the mystery behind the people on the film, and hopefully save her hide.
Why: Gore Verbinski just slams the audience with unsettling images: characters cough up flies, creepy horses jumping to their deaths off cliffs, it’s almost hard to watch and yet not so gory, you have to cover your eyes. You think you know what’s happening but the final twist leads to the ultimate payoff. I’ll admit, I slept with a towel over my TV the night I came home from watching this in the theater.
Scariest Scene: Samara crawls out of the TV.

8. Phantasm (1979)
The character of menacing, disturbing Tall Man (Angus Scrimm) haunts a young boy and his friends with a flying metal ball that had deadly spring-loaded blades.
What: A young boy uncovers the secret behind the village undertaker (The Tall Man) who is building an army by shrinking down the village’s dead and turning them into his zombie army.
Why: The Tall Man is just horrific. This whole film is absolutely disgusting and wrong. When the Tall Man unleashes the dead from under the main character’s bed, or when his creepy silver balls drain the blood out of one victims face — this cult classic is a classic because of The Tall Man and the nightmares he gave us all.
Scariest Scene: Toss up between The Tall Man dream and the infamous silver ball bloodletting.

7. Paranormal Activity (2007)
What: A young couple (Katie and Micah) decides to record the mysterious things happening inside their home.
Why: There was lots of sizzle and hardly any steak in this film, and that’s perfectly okay, as long as Katie gets pulled out of the bed by her heels from time to time. Simple things like the mysterious opening of a door would drive you mad to the point that you were hunting down demon activities on the screen like a Where’s Waldo book.
Scariest Scene: The final scene perfectly encompasses all that made Paranormal Activity a horror hit. Thudding footsteps, screams, and then a body is rocketed towards the camera. The audience is left to their own devices to imagine what happened — but you know it wasn’t good.

6. The Fly (1986)
What: Jeff Goldblum plays Seth Brundle, a mad scientist who has discovered the secret behind teleportation. Constructing a set of awesome telepods, Brundle tests the machines on himself (after flipping his baboon inside out). The experiment appears to be a success... except for one hitch. A fly was in the machine while Brundle was transporting his matter, thus fusing his body with the fly, slowly turning him into an acid-spitting monster.
Why: No one does body horror quite like director David Cronenberg. His work, along with Chris Walas’ horrifying makeup skills, makes one disgusting creature, the Brundlefly. But the decision to turn him into this beast slowly was even more unnerving, and coyly played with the horror that is our own body betrayal.
Scariest Scene: While Geena Davis’ maggot birth was pretty grotesque, the biggest scare has to be the climax where Brundle goes full fly and loses his mind acid vomiting and begging Davis to make him more human (get into the telepods with him).

5. The Thing 1982
What: An alien creature sneaks into an Antarctic research station and slowly starts killing and mimicking the inhabitants. Unaware who is the Thing, and who is human the crew turns on one another.
Why: Rob Bottin’s monsters are legendary, chest cavities became alien mouths, human heads turned into alien spiders, so much wonderful blood and twisty limbs. And the deep paranoia oozed out an excellent trust no one vibe.
Scariest Scene: The blood test scene.

4. The Exorcist (1973)
What: Two priests perform a exorcism on a little girl.
Why: Regan (played by Linda Blair) has to go down as one of the most upsetting villains of all time. The things that demon did to that little girl, goodness. Walking down the stairs on her back, projectile vomit, stabbing herself in the crotch with the crucifix screaming, “Let Jesus Fuck You!,” or simply imitating the voice or Father Karras’ mother there was nothing too appalling for this movie. The Exorcist wasn’t just scary, it was upsetting, you were watching a little girl get violated and violate other characters. Pair that with the haunting theme by Mike Oldfield, and you had a constant feeling of dread.
Scariest Scene: The first ever head demon head twist.

3. Poltergeist (1982)
What: A little girl is abducted by a pack of pissed off Poltergeists.
Why: A great ghost story about the classic American family gone terribly wrong. Everyone is hit in this household because of Craig T. Nelson’s boss decided to build a bunch of homes on top of a graveyard. No one is safe, no room is safe — and yet the parents are trapped in their home, because it ate their daughter. They can’t leave until Carol Anne is back, so they’re forced to endure the horrors.
Scariest Scene: Sure the face melting scene is pretty terrific, and so is the moment where the toy clown comes to life and attacks the kids, but the very best is the calm before the storm. When something as simple as the kitchen table and chairs can be rearranged to cause absolute terror.

2. The Shining (1980)
What: Writer Jack Torrance (Jack Nicholson) moves his family to an isolated hotel during the off season in hopes of getting some writing accomplished. But the evil that inhabits the hotel slowly twists Jack’s mind urging him to murder his wife (Shelley Duvall) and son.
Why: Stanley Kubrick’s take on the Stephen King novel gives the already horrifying read an even creepier twist. Not a single moment is wasted — even the seemingly innocuous conversations with butler Delbert Grady make your stomach turn, as just another demonstration of Jack’s madness. Everything is weighed down with horror, even the simple sounds of a young boy riding his big wheel across the hotel.
Scariest Scene: While we have to give props to the eye opening bathtub rotten corpse make out session, Jack’s novel will always be the most terrifying scene from this film (even if it has been spoofed over and over).

1. Alien (1979)
What: The crew of the Nostromo is woken from their space slumber to investigate a signal from strange planet. Turns out the signal is coming from an alien spacecraft with a collection of pods inside it. One pod opens and the contents wraps itself around a crew members head, it’s all downhill from there.
Why: The tagline, “In space no one can hear you scream,” pretty much sets up why we’ve decided that Alien is the scariest film of all time. The total and complete helplessness of the crew, who are doomed because of their company’s selfish action paired with the aggressive monsters with acid blood and terrifying eyeless faces, makes for some serious horror. There’s no negotiating with this monster — the alien simply wants you dead, the end. No one is safe, no one is spared, and everyone meets a grizzly end (that is of course besides our hero and her cat). The audience gets bludgeoned by KY covered faces and forced into the dark alien hallways of a world no one was familiar with, back in 1979. It changed the way we viewed aliens and forever changed the way people looked at female protagonists.
Scariest Scene: The first time we met the chestburster.

Previously:
io9's 50 Scariest Movies Of All Time: 50 - 41
io9's 50 Scariest Movies Of All Time: 40-31
io9's 50 Scariest Movies Of All Time: 30-21
io9's 50 Scariest Movies Of All Time: 11-20