A cancer expert invented patients for a study which concluded taking common painkillers could protect against oral cancer, it is alleged.
Aspirin was among the drugs studied
Dr Jon Sudbo reportedly made up patients and case histories for the study published in highly-respected Lancet medical journal last October.
Dr Sudbo has not commented publicly on the claims.
But a spokeswoman for Oslo's Norwegian Radium Hospital, where he works, said he had admitted falsifying data.
The revelation comes just days after work published in the journal Science by South Korean cloning expert Hwang Woo-suk was revealed as fabricated.
Hospital spokeswoman, Trine Lind said: "We are shocked. This is the worst thing that could happen in a research institution like ours."
Stein Vaaler, director of external relations at the hospital, added: "He published an article in The Lancet in October last year whose data is totally false, actually totally fabricated.
"His database had been completely fabricated on his computer."
Norwegian daily newsaper Dagbladet reported that of the 908 people in Sudbo's study, 250 shared the same birthday.
Commission set up
The hospital has set up a commission to investigate why Dr Sudbo falsified data and how his material passed a review by other experts.
The panel will also examine previous articles by Dr Sudbo, including two in the New England Journal of Medicine.
The Radium Hospital has halted Dr Sudbo's research at the department of Medical Oncology and Radiotherapy.
Hospital chiefs are now discussing whether he can continue treating patients.
The Lancet study was entitled "non-steroidal anti-inflammatory drugs and the risk of oral cancer."
It concluded that long-term use of the drugs could help reduce chances of oral cancer, including in smokers, but could also bring higher risks of death from heart disease.
Dr Richard Horton, editor of The Lancet, said he would be speaking to the co-authors of the study to seek their permission to retract the paper.
He described the fabrication of data as a "terrible personal tragedy" for Dr Sudbo.
However, he denied that there was anything fundamentally wrong with the process of peer-reviewing contributions to scientific journals.
"The peer-review process is good at picking up poorly designed studies, but it is not designed to pick up fabricated research," he said.
"Just as in society you cannot always prevent crime, in science you cannot always prevent fabrication."