The pervert entertainer, who once painted the Queen, was taken to the Royal Stoke University Hospital from his cell at Stafford Prison.
It is understood the 85-year-old was sneaked in through a side entrance and kept in a secure room in the infectious diseases unit.
A source said the Aussie had X-rays after being admitted over the weekend but it is not clear if he has returned to Stafford Prison, which is a Category C jail.
They added: “He was taken to the Lyme Building where there is a less public entrance than the main ones.
“People are saying he was in a secure room in the infectious diseases unit.
“This is more cut off from the outside world because it is equipped to take the most infectious cases, such as Ebola.”
Harris not due to be released until 2017 after being found guilty of molesting four girls as young as seven between 1968 and 1986.
The disgraced star was caged for five years and nine months by Mr Justice Sweeney at Southwark Crown Court in July last year.
He was found guilty of 12 sex attacks on young girls, including his daughter’s best friend who he targeted from the age of 13.
Officials at the Prison Service and the hospital yesterday refused to confirm whether Harris had received treatment.
A spokesperson for University Hospitals of North Midlands NHS Trust, which runs the hospital, said: “We cannot confirm whether Rolf Harris has been a patient here.”
A Prison Service spokesman added: “We don’t comment on individuals.”
* Last month it emerged Harris was planning to paint a prison mural of his heroes, including Madonna, Sir Richard Branson and Lord Sugar, to “inspire” fellow lags.
There were also fears for the paedophile’s safety after a prison source revealed he hides in the prison library reading crime novels to avoid threats from inmates.