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3 year oldHis 2018 conviction for drugging and molesting ex-basketball player Andrea Constand was overturned on Wednesday.
Judges said there had been a "process violation" by the prosecution, but admitted their ruling was unusual.
Many have expressed concern that the decision could deter women from coming forward in the future.
The decision "is not only disappointing but of concern in that it may discourage those who seek justice for sexual assault in the criminal justice system from reporting or participating in the prosecution of the assailant," Ms Constand and her attorneys said.
Upon his release, Mr Cosby tweeted: "I have never changed my stance nor my story. I have always maintained my innocence."
Mr Cosby is best known for starring in the 1980s TV series The Cosby Show and was once known as "America's Dad".
Dozens of women have publicly accused Mr Cosby of sexual assault, but he was only tried criminally for the incident against Ms Constand. His conviction in 2018 was widely seen as a landmark moment in the #MeToo movement.
In a verdict issued on Wednesday, Pennsylvania's highest court found there was a "process violation" because Mr Cosby's lawyers had made an agreement with a previous state prosecutor that he would not be charged in the case.
The former actor appeared frail as he slowly walked to waiting media outside his home, shortly after being released from prison.
Among Mr Cosby's accusers to speak out against the ruling was Patricia Leary Steuer.
She told CNN: "There were more than 63 of us who came forward in the end. I'm wondering what the purpose was of the 43 years of this ordeal and the trauma that I had and the trauma that my family endured as a result."
Janice Baker-Kinney, who accused Mr Cosby of giving her pills and raping her in the 1980s, told WPVI-TV: "I am stunned, I am shocked and my stomach is in a knot ... One legal ease can overturn this when so many people came forward."
Meanwhile, celebrities have been taking to social media to condemn the decision.
Actor and activist Amber Tamblyn wrote on Twitter: "I am furious to hear this news. I personally know women who this man drugged and raped while unconscious. Shame on the court and this decision."
Columnist E Jean Carroll, who is one of several women to have accused former US President Donald Trump of sexual assault, said: "THIS is why women do not come forward."
Actor Debra Messing tweeted that the decision was "horrifying".
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