The actress, who played spirit talker Tangina in Steven Spielberg's cult 1982 film, was hospitalised in Los Angeles in December (09) after two of her major organs failed.
Internet reports suggested the petite star was close to death after she was reportedly taken off her life support machine, but friends and family insisted Rubinstein was on the mend earlier this month (Jan10).
Her agent, Eric Stevens, has now confirmed she passed away of natural causes at Barlow Respiratory Hospital in Los Angeles on Wednesday (27Jan10).
He tells RadarOnline.com, "She had ongoing health issues and unfortunately they finally overtook her."
A friends adds, "She was very much at peace when she finally rested... The world has definitely lost someone very special."
Poltergeist was Rubinstein's big break in Hollywood. She went on to appear in films like Poltergeist II: The Other Side, Sixteen Candles, Teen Witch and National Lampoon's Last Resort, as well as U.S. TV shows Caroline in the City, Picket Fences and Mr. Belvedere.
From 2000 to 2006 she narrated spooky TV show The Scariest Places on Earth.
Rubinstein was also an activist for HIV and Aids awareness.