A judge will let only one other accuser testify at Bill Cosby's sexual assault trial to bolster charges that the actor drugged and molested a woman at his estate near Philadelphia.
The pivotal ruling by a Pennsylvania judge means prosecutors cannot call 12 other women to try to show that the 79-year-old comedian has a history of similar "bad acts".
Cosby is set to go on trial in June over the 2005 complaint by former Temple University employee Andrea Constand, who is now a massage therapist in Toronto.
Prosecutors reopened the case in 2015 after newly released court documents showed Cosby admitting he gave drugs and alcohol to young women before sex over a 50-year period.
Prosecutors in suburban Philadelphia had asked the judge to let 13 other women testify, a list they developed after reviewing claims by nearly 50 of the accusers who have come forward in recent years.
The defence objected to their testimony, saying the string of old "casting couch" claims are not unique to Cosby and therefore not part of "signature" behaviour.
Montgomery County Judge Steven O'Neill said he carefully weighed the witnesses' value in providing relevant testimony versus the potential prejudice to Cosby.
The one witness who can testify alleges she was assaulted by Cosby in 1996 in Los Angeles.
The ruling is one of two key pre-trial issues in the case.
Judge O'Neill had earlier ruled that jurors could hear Cosby's damaging testimony from Ms Constand's 2005 sexual battery lawsuit.
The deposition runs to nearly 1,000 pages and covers a string of Cosby's extramarital affairs and liaisons dating back to the 1960s.
The revelations from the deposition led to scrutiny of the married father-of-five's treatment of women over the last six decades - from his time as a fledgling comedian to his top-rated turn as Dr Cliff Huxtable in The Cosby Show in the 1980s and beyond.
Cosby's criminal case involves a single encounter with Ms Constand, a former Temple University basketball team employee who has given the media permission to identify her publicly.
She told police he gave her three unmarked pills and then molested her as she drifted in and out of consciousness in early 2004.
In a taped conversation with Ms Constand's mother a year later, Cosby described the sex act as "digital penetration" but refused to say what pills he had given her daughter. In his deposition, he said he had feared sounding like "a dirty old man" on the call.
The additional accuser who can testify worked for one of Cosby's agents and had known the entertainer for six years when he invited her to lunch at his bungalow at the Bel Air Hotel to discuss her acting ambitions.
She alleged he was in a robe and slippers when she arrived and offered her wine and a pill that she consumed after he reassured her it was safe. She claimed she then recalls him sexually assaulting her on his bed.
The defence said she went to the bungalow despite saying she had once rebuffed Cosby's advances before and had no interest in acting.
Among the other accusers who will not be allowed to testify, one said she was an aspiring actress when Cosby allegedly assaulted her at a home near Reno, Nevada, in 1984. Another alleged Cosby drugged and sexually assaulted her in the late 1960s after befriending her and her nine-year-old son.
Cosby's lawyers had argued that he is a wealthy target for the many women he has met during his time in the limelight. His lawyers have said the accusers were being "paraded" before the media by celebrity lawyer Gloria Allred before their accounts are even vetted by police.
"We have seen a barrage of new accusers claiming 'Me, too'," defence lawyer Angela Agrusa said last year, arguing against the "prior bad act" testimony.
Cosby has pleaded not guilty and remains free on bail.
He has attended about half a dozen court hearings since his arrest on December 30 2015 and is expected in court again on Monday to ask that jurors be selected from another county because of pre-trial publicity.
Judge O'Neill wants to start the trial by June 5.