Comedian Bill Cosby has failed to block a civil case accusing him of sexually assaulting a 15-year-old girl at the Playboy Mansion in Los Angeles in 1974.
The California Supreme Court rejected his petition to review the case brought by Judy Huth - meaning her lawyers can now question Mr Cosby under oath.
The 78-year-old is facing a string of sexual assault accusations dating back decades.
He has always maintained his innocence and has never been criminally charged.
Ms Huth alleges that Mr Cosby plied her with alcohol before sexually assaulting her.
Her lawyer, Gloria Allred, described it as a "major victory" and says she intends to take a sworn deposition from the comedian within the next month.
Earlier in the week, the LA police department confirmed that it was investigating "certain complaints against him".
It has already emerged from a previous lawsuit that Mr Cosby admitted giving a woman drugs before sex.
Court documents relating to the case brought in 2005 Andrea Constand - an employee at Temple University in the 1970s - were published earlier this month, after the Associated Press news agency applied to a judge to have the sealed papers made public.
They revealed Mr Cosby had admitted obtaining Quaaludes from several doctors to give to women before sexual encounters, but did not take them himself.
Mr Cosby is now suing Ms Constand for breaching a confidentially agreement after the New York Times obtained a full copy of the deposition.
Dozens of women have accused the comedian of sexually assaulting them but most of the claims are barred by statutes of limitations. They restrict the length of time in which legal actions can be taken after an alleged crime has been committed.
The accusations, which Mr Cosby has described as "fantastical" and "uncorroborated", have led to some of his stand-up shows being called off and the cancellation of some TV projects.
Timeline of allegations against Bill Cosby
2002: Lachele Covington, a 20-year-old actress, reportedly files a police report saying she had been inappropriately touched. No further action was taken.
2005: Andrea Constand sues Mr Cosby for sexual assault. The case is eventually settled out of court in 2006.
2014: Over the year, dozens of women make public accusations that Mr Cosby sexually assaulted them. Live shows are cancelled across the country amid protests
November 2014: TV network NBC scraps plans for a new show with the comedian following allegations by TV presenter Janice Dickinson that he had assaulted her in 1982. Repeats of the Cosby Show are also pulled from cable TV
December 2014: Judy Huth sues Mr Cosby for molesting her in 1974 when she was 15 years old. Mr Cosby counter-sues, claiming she is trying to extort money from him
May 2015: Mr Cosby speaks publicly about the allegations for the first time. "I can't speak; I just don't want to argue; I don't talk about it," he told ABC News.