In an interview due out next week, the 67-year-old told an AARP reporter that she was diagnosed eight months ago.
Ronstadt says she can't sing a note because of the disease.
She started showing signs of the debilitating illness as long as eight years ago but says she had chalked up her inability to sing to other ailments.
She said she was "completely shocked" when she finally saw a neurologist and was diagnosed with Parkinson's disease. "I wouldn't have suspected that in a million, billion years."
Ronstadt sold tens of millions of records starting in the 1970s with pop hits like "You're No Good" and "When Will I Be Loved." But she also segued into country, pop standards and mariachi music, among other genres.
In addition, the singer was known for her romances with California Gov. Jerry Brown and filmmaker George Lucas.
Her autobiography will be released next month, but makes no mention of Parkinson's or the loss of her voice, according to AARP.
The Associated Press contributed to this report.