Judge Terry Ruckriegle said no witness during three hearings had convinced him that the woman had waived her confidentiality rights by telling others about her medical conditions and treatment.
Ruckriegle also threw out defense subpoenas seeking records from three health care providers.
Bryant faces four years to life in prison or 20 years to life on probation if convicted of felony sexual assault. The Los Angeles Lakers star has said he had consensual sex with the woman last summer at the Vail-area resort where she worked.
The judge acknowledged the woman had discussed her conditions and treatment in general terms with friends and relatives, but said he believed it was clear she had no intent to waive confidentiality.
"The victim never revealed the specific nature of her medical treatment, the substance of her conversations with the medical providers nor other confidential details of her condition and medical treatment," the judge wrote.
Ruckriegle also rejected defense arguments that the woman waived privacy rights by talking with Eagle County sheriff's Detective Doug Winters, who interviewed her shortly after the alleged assault.
The woman's attorney, John Clune, declined to comment. Defense attorney Hal Haddon did not return a call, and prosecution spokeswoman Krista Flannigan said only that prosecutors were pleased.
"This is a defeat for the defense because it precludes Bryant's lawyers from presenting to jurors what is probably the best evidence there is about the alleged victim's mental condition before the incident last June. But the defense still will be able to bring witnesses onto the stand to talk about that condition," says CBSNews.com Legal Analyst Andrew Cohen.
"This is good news for prosecutors and for the alleged victim but it doesn't wipe this mental health issue out of the case or out of the trial," says Cohen. "The medical records are out -- the written evidence remains protected by the doctor-patient privilege -- but the defense still can bring witnesses to the stand to testify about what the alleged victim told them about her mental state of mind."
Bryant's attorneys have said in court filings they believe the woman's medical records could undermine her credibility and demonstrate she had a "scheme" to falsely accuse the Lakers star. They say she twice attempted suicide in the months before meeting Bryant, and had been prescribed anti-depressant and anti-psychotic drugs.
Prosecutors have argued that none of the information contained in her medical records is relevant to whether she consented to sex with Bryant.
Analysts said the ruling was not surprising, considering strong state laws protecting confidentiality and a 2002 Colorado Supreme Court ruling that told judges they cannot review medical records — even behind closed doors — without consent.
"This is definitely an important victory for people who get medical treatment that don't want to lose the privilege just because they've decided to talk to other people or confide in family and friends for support," said Karen Steinhauser, a former prosecutor and visiting professor at the University of Denver law school.
Larry Pozner, past president of the National Association of Criminal Defense Lawyers, said the defense still can seek testimony from people who have direct knowledge about the woman's purported suicide attempts and prescription drug use.
"The defense has a bathtub full of evidence on her suicide attempts that is not in the medical records — it's just plain old-fashioned (eyewitness) testimony," Pozner said.