Canada's highest court has upheld a sexual assault conviction in the case where the victim thought she was having sex with a man's identical twin brother.

After a party one night in September 2006 the woman, who had consumed most of a bottle of wine, went to sleep in the bed of a man with whom she had a consensual sexual relationship.

Later, she awoke to someone having sex with her and assumed it was the man with whom she had a relationship.

She called out the man's name several times and when he said nothing throughout the act she turned on the light, only to discover it was the man's twin brother.

He appealed his sex assault conviction, saying the trial judge was wrong in finding the mistaken identity meant she didn't consent to sex.

The Court of Appeal for Ontario disagreed, upholding the conviction earlier this year, and today the Supreme Court of Canada declined to hear the man's appeal of that decision.