Allegations of cheating in an exam have Otago medical students fearing that everyone will be forced to resit it.

Student magazine Critic Te Arohi quoted a letter from Dunedin School of Medicine dean Prof Barry Taylor to third year students saying the "integrity of the exam has been compromised" and all results had been withheld pending further investigation.

Prof Taylor called the alleged cheating "very unprofessional behaviour".

He said the school had a duty to the public to ensure its students reached "an appropriate level of competency".

The exam in question was the "objective structured clinical examination", which Critic said was a practical examination where students were tested on clinical skills.

Students take the exam in groups at different times and it is alleged after finishing the exam students passed on information to those taking it later.

Students quoted by the Critic feared everyone would have to resit the exam and said there was a history of students passing on information to later groups.

"It's been like that forever," one said.

Students had been asked to help the university with its investigation, but one student said they were "definitely not gonna tell on someone".

The Otago Daily Times has sought comment from the University of Otago.