Alien Sydrome is a shoot'em up developed by Sims Co. and published by Sega. It is based on the eponymous arcade game, but not a straight port of it.

The story is actually a sequel to the arcade game's. Five years after the events of the arcades version, the aliens return and infest a spaceship called Dagal. Ricky and Mary, the heroes from the original game, come to the rescue.

The formula has not been changed compared to the original. You go through each level in order to rescue hostages.The game uses a top-down view. Aliens are spawning constantly and you die on one hit. You have a gun with infinite ammo and you can pick up other weapon which are place on the walls. Once ouy have rescued enough hostages, the exit will open and you can leave the level. There is a time limit to beat each level, and you have to fight a boss before reaching the next level. the graphic sets, enemies and level layouts differ from the original game. Also, you can call a level map which shows the position of all remaining hostages at any time, while you had to pick up an item for that in the original.