You can see the party with the #instagramdown hashtag.
Facebook, which owns the photo-sharing site, said in an email statement and posted on Instagram's Twitter feed, "We're aware that some users are having trouble accessing their Instagram accounts. We're working quickly to fix the issue and should be 100 percent up shortly."
Update, 3:48 p.m. ET: Added statements from Facebook and Instagram.
Update, 4:43 p.m. ET: Added the news that it was up and running as usual.