Disgraced US TV legend Bill Cosby appealed a Pennsylvania judge's refusal to dismiss a sexual assault case against him, according to a document seen by AFP.

The 78-year-old actor and comedian is accused by dozens of women of sexual assault dating back decades, but the vast majority of cases have expired under statutes of limitations.

The small number of cases that are proceeding are playing out in civil court -- except in Pennsylvania where Cosby is standing trial for the first time on a criminal sexual assault charge.

Cosby's appeal centers on a decision in Pennsylvania earlier this month by Judge Steven O'Neill, who threw out an attempt by the actor's lawyers to have the case dismissed.

Cosby's lawyers filed their notice of appeal against that decision to the Superior Court of Pennsylvania on Friday.

The sexual assault accusation against Cosby dates back to 2004 and the matter was originally settled in 2006 by a civil suit.

The accusation was brought by Andrea Constand, who said Cosby forced himself on her at his suburban Philadelphia home in 2004. Prosecutors say he urged her to take pills and drink wine, leaving her unable to resist as he made his move on her.

In a deposition Cosby gave as part of the civil suit, he admitted giving Constand a pill, but said all relations with her were consensual and accused her of lying about the assault.

Prosecutors reopened the case last year, claiming that new evidence came to light in July.

Cosby's legal team argued that that violated a 2005 agreement that he would never be prosecuted over the allegation of assault made by Constand, a former employee of Temple University in Philadelphia.

The avalanche of accusations against Cosby have led television networks to back away from projects connected to him, and several universities have stripped him of honorary degrees.

On Friday, Cosby also appealed another decision in which the judge refused to disqualify the lead prosecutor from participating in an eventual trial.