Bill Cosby sexually assaulted a teenage girl at the Playboy Mansion in 1975, a jury in California has found.
The decision on Tuesday is the first civil ruling against the TV star, who has been accused of using his fame to prey on dozens of women over several decades.
Judy Huth, now aged 64, was awarded $500,000 in damages after the jury found Mr Cosby, 84, meet her on a film set when she was 16 years old and plied her with alcohol before molesting her.
Mr Cosby was jailed in Pennsylvania for drugging and molesting a woman in a separate criminal case in 2018, but was freed last year when his conviction was overturned on a technicality.
Over a two-week civil hearing, which Mr Cosby did not attend, lawyers said Ms Huth and her then-17-year-old friend Donna Samuelson, were taken by Mr Cosby to Hugh Hefner's mansion after meeting them on a set.
They were told, when alone with her, Mr Cosby began kissing Ms Huth and tried to put his hands inside her clothes. He then allegedly pulled down his trousers and forced her to perform a sex act on him.
Ms Huth had repressed memories of the assault for years, lawyer Nathan Goldberg said, but the memories resurfaced when other women began accusing him of assault.
“It was like a cork popped out of a bottle,” said Mr Goldberg at the start of the case. “Memories came rushing to the surface … she became overwhelmed by memories of Mr Cosby and what he had done.”
She originally filed her lawsuit in December 2014, but the case was put on hold while various criminal investigations played out.
The civil trial was shown a videotaped deposition of Cosby taken in 2015 in which he denied the assault and insisted that he would never engage in sexual activity with an underage girl.
His lawyers made much of apparent discrepancies in Ms Huth's story, including that both teenagers spent up to 12 hours at the mansion after the alleged assault.
They also argued that Ms Huth originally claimed the attack happened in 1974 when she was 15, but later said it had happened the following year.
The case was never prosecuted criminally as the statute of limitations had passed by the time Ms Huth spoke to police.
California law allows adults who say they were sexually abused as minors, but have only recently become aware of the damage, to bring civil cases years after the statute of limitations would normally have expired.
Mr Cosby was a big star on TV in the US and globally in the late 20th century, peaking as father Cliff Huxtable on “The Cosby Show” 1984 to 1992.
About 60 women have accused Mr Cosby of being a serial predator who plied victims, many of them aspiring actors and models at the time, with sedatives and alcohol over four decades.