Psychological horror, without a doubt. Some of the best movies fit under that genre.

It's most definitely a horror film. And a damn creepy and unsettling one at that. There are few things that are worse or more scary than the demons of the human mind.
You've seen Guy Standeven in something because the man was in everything.

Psychological horror dealing with spiritual possession, it might not be Scream or Nightmare on Elm Street but it's still a horror
We don't have a dog. That was just some really violent sex.

Pretty sure you can interpret it both ways lol.
I've not seen this film in a few years (I plan to watch it again tonight)
but I could have sore there were supernatural elements in it.

What Gordon and Mary both hear was the voice of insanity. Both snapped when faced with what was to them severe emotional stress. Mary cut up by her glass doll given to her as a Christmas present, and Gorden when faced with his failing business and sleep deprivation due to constantly sick baby.
This movie was set in an asylum for a reason, rather than a haunted house.

Then why did Gordon hear Simon's voice (the same voice Mary heard)? Pretty sure they were both possessed by some evil entity (Simon).
Someone here said it better than I did:
He was possessed by "Simon", the same spirit that possessed Mary. Simon possessed Mary and had her kill her family. When Mary died at the asylum, Simon was released and remained until another of the "weak and the wounded" was receptive to possession. That would be Gordon, who was already exhausted by the issues with the baby, job and marriage. As soon as Gordon enters, you hear Simon introduce himself with a "Hello Gordon". That's when the possession began.
CG gore is the worst thing that has ever happened to the horror genre.

Excuse me? It's a ghost story? Uhhhhhh, no. It's a story about a MENTAL BREAKDOWN. There is 0 mention of ghosts or hauntings. It's an INSANE ASYLUM and we saw an up close depiction of a man coming unravelled at the seams and losing his mind. THAT'S IT, THAT'S ALL. No ghosts.

Just because the movie was subtle and complex, doesn't mean it wasn't horror. It's a "ghost story" in the broad sense which counts.

Let me get this straight, OP. So because YOU personally didn't feel scared that somehow negates the fact this is a horror movie? Do comedies cease to be comedies if you don't find them funny? What about an action movie that doesn't excite you? Is that not an action movie any more?
Your personal feelings on the film have nothing to do with the genre. You're not that important.

When I first saw this film, I thought it had wasted potential and was average at best.
However, I found myself thinking about it as I was lying in bed at night, generally creeping myself out. This led to me watching it again (and again!) until I became a bit obsessed: watch it alone in the dark- it scares the beep out of me when I do that!

Of course it's a horror movie. Specifically, psychological horror. It gave me a feeling of being unsettled. But even if it hadn't, being scared is not a requisite for being a horror film. And I'm glad it barely showed anything.
"America isn't ready for a gay, mexican chicken sandwich"

It was most definitely a horror, along the lines of classics like The Shining, and The Changeling.

I wouldn't call it "horror," either.
It's a (tepid) psychological drama.
(There's no hard and fast definition of what's what, of course.)

Yeah, so could I. People think it's original, because they're too young to know the original source material he ripped off.

Also watch insidious if you guys wanna actually see a good horror movie.
Man, I could take Insidious and show you minute by minute what the film is a rip-off of, and where he stole all his monsters and subplots. There is not a second of originality in Insidious.

The only thing that sucks and is stupid is you and your post.

You don't rememberer the ridiculously flamboyant blacksmiting demon?

In what way do you find the ending ''ridiculously out of place''?

Agreed.
Though to be honest, I was genially creep-ed by the film, that was until the ridiculously out of place ending ruined it for me.

Yep, gotta agree with vol on this one. Hollywood horror flicks are usually the worst. Blah.

You missed one word - Hollywood.
So it would say ''Insidious has been one of the better ghost films nowadays compared to other current HOLLYWOOD films''
Otherwise it doesn't make any sense, since the movie itself is a third class piece of sif compared to all curent horror films.
Hollywood is not the only movie industry out there you know. And what is more, so far horror movies are concerned, Hollywood usually sucks

Speed you're a moron..Insidious has been one of the better ghost films nowadays compared to other current films

Haha, that is your recommendation of a good horror movie? Yikes. In a word, that movie was garbage.

Naw, I disagree. Asian horror is all child ghosts and creepy women with long, black hair. That stuff got old for me quick. After you've seen a few Japanese ghost horror movies, you think, "Man, this stuff is starting to all look alike."