Alien Syndrome (エイリアンシンドローム, Eirian Shindorōmu) is a run and gun video game developed by Sega and released in arcades in 1987, and later ported to the Master System the same year.

The game utilizes a side-scrolling feature that allows the player to take control of either a male (Ricky) or female (Mary) soldier whilst hunting aliens and saving hostages before they run out of time.

Two players control two soldiers, named Ricky and Mary, who fight their way through large eight-way scrolling levels while rescuing their comrades who are being held by aliens.

Alien Syndrome features two player simultaneous gameplay and pickups, including better weapons and maps of the current level.

In Japan, Game Machine listed Alien Syndrome on their May 15, 1987 issue as being the third most-successful table arcade unit of the month.