Lawanda Jackson, the former employee of UCLA Medical Center had been paid at least 4,600 dollars by the National Enquirer for the details from the medical centre.
Sentencing is due in May, reports BBC.
Prosecutors said Jackson had worked there for 32 years, only selling records in recent years.
The 49-year-old resigned from her administrative job in July 2007 before she could be sacked, they added.
The National Enquirer was not available for comment.
The paper began depositing cheques in the account of Jackson's husband in 2006, prosecutors said.
She faces up to 10 years in prison and a 250,000 dollars fine for breaking medical privacy laws for commercial purposes.