NES
The Konami Code
To receive one Speed-Up, Missiles, two Options, and Barrier, pause the game and enter the famous Konami Code: 
, and unpause the game. This can be performed once, plus one more time for each time a Big Core boss is destroyed before its core turns red.
Continue code
To continue the game from the start of the last stage you visited, enter the following code at the Game Over screen: 
.
Secret message
Press and hold the and buttons on the second controller while you reset the machine.
Warps
There are three mechanisms in the game that allow you to warp ahead past one stage. They are only found in stages 1, 2, and 3. Warps are activated if you fulfill the proper conditions for each stage and defeat the Big Core on that stage. Once the warp is activated, you will rush through space while you encounter randomly positioned spinning Moai heads that you must dodge. The most you can warp is two times, once from stage 1 to stage 3, and again from stage 3 to stage 5.
Stage 1 warp: To activate the warp to stage 3, you must destroy each of the four hatches that appear on this stage when the thousands digit of your score is even. Of the four hatches, three are on the lower portion and one is on the upper portion.
Stage 2 warp: To activate the warp to stage 4, you must destroy the Big Core within two seconds of the core turning blue. This is only possible with very well placed shots from lasers.
Stage 3 warp: To activate the warp to stage 5, you must destroy 10 or more Moai statues. Use missiles to destroy bottom lying faces, and double-shot or options to destroy top lying faces.
Stage bonus
The first four stages contain two locations that you can fly the Vic Viper through to collect bonuses. One is a 5000 point bonus that you can collect unconditionally. The other is a 1-Up bonus that you can only collect if the thousands digit of your score is even. The fifth stage contains no bonuses, but the sixth stage does contain a 1-Up bonus. Remember that in order to collect the bonus, you must literally pass through the location indicated in the screenshot.
PC-Engine
Instant power-up
To receive one Speed-Up, Missiles, four Options, and Shields, pause the game and enter the famous Konami Code: 
, and unpause the game.
30 lives
To begin the game with 30 extra lives, press and hold at the title screen, and press three times. Then start a new game.
MSX
Secret bonus stages
The MSX version of Gradius contains hidden entrances to secret bonus stages. If you occupy the correct location of four particular stages, you will be sent to a bonus stage similar in nature to the second stage, and advance to the next stage upon its completion. The bonus stages are analogous to the bonus stages found in the Super Nintendo conversion of Gradius III. They contain two new types of capsules; green and yellow. Green capsules provide you with one extra life. Yellow capsules provide you with an increasing number of bonus points, starting at 100 and increasing to a maximum of 10,000 points, but only if you never fail to collect a single capsule. If one yellow capsule scrolls off the screen, the point value will reset to 100. Some locations contain several yellow capsules and you must remain in place in order to collect all of them. Below are indications of every bonus stage entrance.
| Stage 2 | Stage 3 |
|---|---|
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| Stage 4 | Stage 7 |
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Play as Twinbee
Most MSX consoles contained not one, but two cartridge slots. If you place Konami's TwinBee cartridge in the second slot while you play with Gradius in the first cartridge slot, you will play through the game as the TwinBee ship. Power-up capsules will take the form of bells (although they will not "fall" to the left side of the screen, as they do in TwinBee or Parodius) and your Options will be glowing outlines of TwinBee. Even the shield will look different.