A new patient-booking system at two Bristol hospitals has been described as "potentially dangerous" by consultants, the BBC has learned.
It has led to some patients missing their operations and the wrong patients being booked for operations.
Emails from bosses at Frenchay and Southmead hospitals, seen by the BBC, said staff should be "vigilant" to check lists were "completely accurate".
North Bristol NHS Trust said it was due to software being used incorrectly.
BBC Points West's health correspondent Matthew Hill said emails sent by consultants to hospital bosses claimed operation lists printed by the system were "complete fiction" and "potentially dangerous".
One consultant also told the BBC he had been put down to operate on patients from a completely different speciality.
The trust said there had been "teething problems" but admitted there had been "more problems than anticipated".
In an email to staff the trust said the change of system had been "a very big change" so there was "no surprise" there had been difficulties.
A trust spokesman said there were a series of problems around outpatients and the associated clinics and some of the data moved from old systems had not migrated as planned.
"We need to ensure that we rebuild and recreate the clinics to match what people expect them to be on the ground," he said.
"In theatres we have had some issues but have absolutely ensured from the outset that clinical safety has been at the top and have ensured any risks and issues have been mitigated."
North Bristol NHS Trust, which provides hospital and community healthcare to the residents of Bristol, South Gloucestershire and North Somerset, is responsible for running Southmead and Frenchay hospitals.