Drummer Marco Minnemann (The Aristocrats) had never listened to Dream Theater before Jordan Rudess invited him to audition.

Before Mike Mangini was officially announced as the new Dream Theater drummer in 2010, he had already worked together with James LaBrie on his three first solo releases. These include Keep It To Yourself, MullMuzzler 2 and Elements Of Persuasion.

Portnoy wrote "Repentance" (the 5th song from 2007's "Systematic Chaos") as the fourth part of his Twelve-step Suite, a collection of songs from various Dream Theater albums which revolve around his journey through Alcoholics Anonymous. The song discusses steps eight and nine of the process, which deal with making a list of people whom one has wronged and, if possible, making direct amends with them. Portnoy, who as of 2007 had been sober for 7½ years, invited friends and fellow musicians Mikael Åkerfeldt, Jon Anderson, David Ellefson, Daniel Gildenlöw, Steve Hogarth, Chris Jericho, Neal Morse, Joe Satriani, Corey Taylor, Steve Vai, and Steven Wilson to record spoken apologies, regrets, and sorrows of their own, which were featured throughout the song. Portnoy was disappointed that Dave Mustaine, Geoff Tate, Bruce Dickinson and James Hetfield declined his invitation, but was pleased with the final list of contributors.

On the live CD/DVD "Once In A LIVEtime" there is a tribute to the Binary Sunset theme from the Star Wars franchise. In the segue from "Just Let Me Breathe" into "Voices" John Petrucci playing the first half of the theme.

A shortened version of the song Pull Me Under (clocking at 4:48 instead of 8:11) also featured a music video which alternated between clips of the band performing and an obscure storyline about someone, who is often described by band members and fans as a "wolfman." The band members were reportedly unhappy with the storyline, saying that it doesn't have anything to do with the song's subject matter. Lead singer James LaBrie can be seen wearing a Napalm Death shirt in the video. According to drummer Mike Portnoy that shirt actually got the band connected with Napalm Death.

A distinctive feature of the song Pull Me Under, from their second album "Images And Words" is its lack of a conventional ending. The song simply stops at 8 minutes and 11 seconds. This abrupt ending was corrected in their Greatest Hit compiliation, with the song now stopping at 8 minutes and 13 seconds. A later Dream Theater song, "Raw Dog" (from the "God Of War: Blood & Metal album"), ends abruptly, similar to "Pull Me Under".

Despite the band's being forced to change their name, Dream Theater adopted a custom logo (known as the Majesty symbol) and wordmark which has appeared on the vast majority of their promotional material and on the front cover of every Dream Theater studio album. The Majesty symbol is derived from Mary, Queen of Scots' mark, which was re-worked by Charlie Dominici for use on the album artwork for When Dream and Day Unite.
In September 2010, a fan of Dream Theater discovered that all of the letters of "DOMINICI" fit together perfectly into the Majesty symbol. When Charlie discovered this, he laughed and mentioned that "it only took them 25 years to figure out the 'Dominici Code!'" This has earlier also been discovered as shown on the comment section of DTFAQ and in the DTNorway Podcast Episode 2 from 2008, with Charlie Dominici.

An edited version of the song "A Change of Seasons" was used in a downhill skiing feature during the 2002 Winter Olympic Games.

On the track "In The Name Of God", there is a Morse code passage that, when translated, says "Eat my ass and balls" which is known as Mike Portnoy's catchphrase.

Almost half of the songs from "Metropolis Pt. 2, Scenes From A Memory" are featured in "The History Of Trunks", a Dragon Ball Z movie.

"The Great Debate", off of Six Degrees of Inner Turbulence, was to be named "Conflict At Ground Zero" but was changed due to the 9/11 attacks. To add to it, "Disappear" was originally called "Move On" before changed.

At Dream Theater's Salt Lake City show, Governor Jon Huntsman, Jr. signed a proclamation making July 30, 2007 "Dream Theater Day".

Petrucci first played guitar at age 8 when he noticed his sister (who was taking organ lessons at the time) was allowed to stay up past her bed time to practice. He soon dropped it when his plan failed. At age 12, he began playing again when he was invited into the band of his friend Kevin Moore, who would later become the first keyboardist of Dream Theater.

The intro and outro samples in "6:00" off the album "Awake" are taken from the John Huston film The Dead, which originally was a book with the same name by James Joyce.

Released on September 11th 2001, the original cover of 'Live Scenes From New York' displayed a flaming apple wrapped in barbed wire with the skyline of New York (including the Twin Towers!) engulfed in flames. On the same day two planes crashed the WTC, prompting the original issue to be recalled and later reissued with a different cover. Some copies with the original artwork still exist, and are now a rare collectors item.

The building that is shown in the back cover of their album "Metropolis Pt. 2: Scenes From A Memory" is actually the "Bear Tracks Studio" where the band spend many years recording their stuff.

Mike Portnoy wrote that he wanted to be the next "Neil Peart" (drummer of Rush) when he grew up in his school yearbook.

"Dream Theater" was the name that Mike Portnoy's father suggested for the band, taken from a movie house in Monterey, California.

James LaBrie did not use his first name (Kevin) because it was confusing enough to have two Johns (Petrucci and Myung) in the band. Just imagine having two Kevins (Moore and LaBrie) as well!

Nicky Lemons is Derek Sherinian's alter ego. Supported by the Migraine Bros (Petrucci and Portnoy), his hit song "I Don't Like You" was played as an encore to many shows during the Touring Into Infinity world tour. The ficticious album entitled "Ugly American" was planned for release, but unfortunately due to lack of support the project was scrapped.

On Halloween night of 2002, John Myung did a full out football tackle on James LaBrie, while wearing his bass, during the show. As it turns out, it was a dare that nobody thought that he would do. He was paid a couple hundred dollars after for that stunt.

The "DT Grandma" is a lady of about 60 who is probably a bigger Dream Theater fan than most other people in the world! Her name is Patricia McLoughlin.

Nightmare Cinema is a warped version of Dream Theater. It features John Petrucci on drums, John Myung on keys, Mike Portnoy on bass, Derek Sherinian on guitar, and James LaBrie on vocals.

The song "Ytse Jam" comes from spelling their original name, Majesty, backwards. It is pronounced as "It's a Jam", which it is.

Mike Portnoy has been named "Modern Drummers" best drummer of the year for twelve consecutive years.

John Petrucci, John Myung and Mike Portnoy are all married to members of the power/thrash band Meanstreak.