A spokeswoman for the singer said the 21-year-old had cancelled her Bangerz concert in Kansas City, Missouri.
Publicist Meghan Prophet said in a statement that Cyrus is on "medical rest" at her doctors' advice.
Cyrus said on Twitter that she was heartbroken to miss the show. She also posted a photo of herself wearing what appears to be a hospital gown.
Tickets for the concert at Sprint Centre are being refunded.