The appearance of Longclaw in Paramount’s Sonic the Hedgehog films is reminiscent of the tiles that resemble an owl's head in the Labyrinth Zone from the original Sonic the Hedgehog. In fact, the first film's opening scene features the tile design engraved on a rock as an Easter egg, further hinting at the connection.

Sonic was originally planned to have a human girlfriend called Madonna, whose design was directly based on the sexually provocative American pop singer of the same name. In line with this, character designer Naoto Ohshima designed Madonna to be attractive and to chase Sonic around (similar to how Amy Rose acts in later games), which he described as a "male fantasy". Aside from concept art, Madonna's only known appearance was in a 1990 tech demo for the TeraDrive, a Japan-exclusive IBM PC with a Sega Mega Drive integrated into it. There are two separate claims as to why Madonna was removed. Programmer Yuji Naka originally claimed in 1993 that Madonna's planned role was to be a damsel-in-distress, with Sonic needing to save her, and that she was ultimately dropped because the team wanted to move the series in a different, more orthodox direction to set it apart from Mario. However in 2009, Sega of America product manager Madeline Schroeder claimed to be the one who removed her as part of an overall effort to "soften" Sonic's image for younger audiences and foreign countries under the belief that Madonna was too Japan-esque. In 2015, Madonna would be reimagined by comic book writer Ian Flynn and appear in Archie Comics' Sonic the Hedgehog comic book series, having been redesigned to be an agent of G.U.N.'s C.L.I.P. division named "Madonna Garnet".

The title screens of Sonic the Hedgehog and Sonic the Hedgehog 2, with Sonic (a character known for his super speed) posing and waving his gloved hand inside of a ring lined with stars and a ribbon banner at the bottom, could possibly be taken from the logo of the 1981 anime adaptation of the Akira Toriyama manga "Dr. Slump" and its speedy protagonist Arale. It should also be noted that the ring surrounding Sonic has giant wings protruding from its sides, which appear to reference the angel wings on Arale's cap that also feature in the intros to the anime and some of the Dr. Slump films.

While it's not known if any Sega employees have commented on this connection, it was acknowledged in the form of a small cameo appearance where Sonic gets outrun by Arale in the 1993 sequel manga "The Brief Return of Dr. Slump".

It's possible to play the game using an Atari 2600 controller, as every button besides start works as a jump button, and thus the game is fully playable despite the controller only having a single button.

Sonic's graphic on the title screen of Sonic the Hedgehog has a belly that is obscured by the logo's ribbon. This is a leftover of the animatic of Sonic's appearance on the title screen. On earlier, less accurate emulators, including Sega's own emulator made for Sega Smash Pack Volume 1 on Dreamcast, a common error would involve Sonic's belly hanging over the ribbon.

In issue 260 of Nintendo Power, Yuji Naka revealed that the initial concept for Sonic the Hedgehog's gameplay came from playing level 1-1 of Super Mario Bros. over and over again as fast as he could, since you always had to play the level first regardless of whether you used warp zones or not.
"I always tried to get through the level as fast as I could. And that inspired the initial concept for Sonic the Hedgehog."

In Sonic the Hedgehog, there is an unused "PRESS START BUTTON" graphic. This would eventually be used in an exclusive revision of the game included in the Sega Top Ten compilation cartridge for Brazil and Asia. This version of the game is otherwise identical to the original release.

The file header (the game's name used as an introduction for its code) for Sonic the Hedgehog is supposed to have a line break in the middle, so it reads as:


However, this line break was done through spaces instead of an actual line break, so if one plays Sonic the Hedgehog on an emulator that shows the file header name (such as Kega Fusion), it will instead read:


[Note: periods added due to VGFacts automatically removing multiple rows of spaces.]

Connecting Sonic & Knuckles to the first Sonic the Hedgehog will not allow you to play as Knuckles in the latter game. This was not due to hardware limitations as is commonly believed, but rather because the game's development team felt that, while Sonic 2 was designed with Super Sonic's flight in mind and thus had verticality to its levels fit for Knuckles' climbing, Sonic 1 was not, and therefore simply was not fun to play as Knuckles in.

Hirokazu Yasuhara was going to go to America to establish a new development team but because of the Gulf war between Iran and Kuwait, his trip was delayed. Yuji Naka and Naoto Oshima noticed him being upset and decided to let him join their team temporarily until he leaves. He ended up staying for a year to design the levels for major games such as Sonic the Hedgehog.

In an early version of Sonic The Hedgehog shown in a pilot episode for the TV game-show "Nick Arcade", a rolling ball can be found towards the start of Green Hill Zone Act 1. This was removed from the game's final release.

In the original international release, a short cut taken to the finish in the Labyrinth Zone would only allow the player to collect a total of 49 rings, missing 1 ring from going to the special stage. However, in the Japanese version, a ring was added so that people could get to the special stage if they went this way.

The Japanese version of the game has more parallax scrolling layers. An example would be that the clouds in some of the zones move across the screen, while the international version the clouds are stationary. The Labyrinth zone also has an underwater wave effect in the Japanese version. The only zones that were not changed were the Starlight zone and the Final zone.

Within the game's data is a set of unused sprites showing Sonic shrinking or falling away from the screen.

In the game's code there exists a sprite of a Goggle monitor, and some matching goggles to go with it. There is also an unused sprite of Sonic holding his breath, meaning these were likely once an underwater power up.

Scrap Brain Zone was originally known as 'Clock Ork Zone'. It's believed the name was changed because it was planned to be called 'Clock Work Zone', but no 'W' existed in the game's zone title font.

The Japanese band "Dreams Come True" are credited with composing the game's entire soundtrack. To promote their first tour, the band had concert posters with Sonic the Hedgehog on them, and painted Sonic on the side of their tour bus.

The game's soundtrack was composed on an Atari computer.

In early screenshots of the Genesis game, a UFO could be spotted, but was not present in the final game. Yet when Sonic the Hedgehog was released in 2005 for mobile phones, the UFO sprite was found hidden away in the files, but still unused.

There are hidden embedded Japanese staff credits on the "Sonic Team Presents" screen. With the aid of a palette editor or cheat code, one can hide the title card and invert the colour of the background to make it visible.