An investigation is underway at a Suffolk hospital to find out why 29 patients waiting to see a specialist were not seen within 13 weeks.
Ipswich Hospital has written to the patients to apologise
Ipswich Hospital NHS Trust said it had apologised for not seeing the patients within the nationally-set time frame.
One of the possible reasons being looked at for the delay is that their details were filed incorrectly.
Trust chairman Mike Brookes and chief executive Andrew Reed said they had ordered an immediate inquiry.
Mr Reed said: "We are very disappointed and unhappy about what has happened.
"The evidence we have gathered already leads us to believe that a failure to follow the correct procedure is at the heart of the problem."
The hospital said that more than 270,000 referral letters from family doctors to consultants are received by the hospital every year.
It added that the people affected did not have life-threatening conditions.