Stephen Sutton told supporters on Facebook he had returned to hospital after developing "breathing difficulties" on Saturday night.
The 19-year-old has collected more than £3.22 m for the Teenage Cancer Trust since posting a picture of himself in hospital last month with a goodbye message when he believed he was close to death.
However, after making what Stephen describes as "a miraculous recovery" and after successful surgery, he was discharged from Birmingham's Queen Elizabeth Hospital on May 2.
However, commenting on his Facebook page he was again posting from hospital.
He said: "Unfortunately. I've ended up back in hospital. I had some breathing difficulties starting last night and after going to A&E have been admitted back to a ward for monitoring.
"There's no immediate panic and I'm currently quite stable - I have been put on nebulisers and other meds which are currently helping my symptoms."