A backlog of 24,000 patients needing hospital appointments in Cambs, Norfolk and Suffolk, must be cleared by the end of the year, a health body has warned.
The Norfolk, Suffolk and Cambs Strategic Health Authority (SHA) says if they are not seen, the hospitals will miss government waiting targets.
Hospitals told the BBC that they expected to meet the targets.
The concerns over the backlog are in an SHA report which goes before its public board meeting on Wednesday.
Outpatients needing hospital appointments by end of year
Cambridge University Hospitals 2,842
Hinchingbrooke Health Care 1,205
Ipswich Hospital 2,002
James Paget Healthcare 1,951
Queen Elizabeth, King's Lynn 1,549
Norfolk and Norwich University Hospital 3,952
Papworth Hospital 16
Peterborough and Stamford Hospitals 2,689
West Suffolk Hospitals 2,222
PCTs and Mental Health Partnerships 239
In the report, SHA director of performance and finance Steve Clarke, said that in relation to outpatients there was "still a significant number of patients who need to be offered appointment dates".
The report says there are 18,667 outpatients who need to be seen by the end of the year to meet the government's 13-week wait target, with 2,441 still without an appointment date.
In relation to inpatients, Mr Clarke said: "There are a sizeable number of patients who need to be admitted for treatment before the end of December.
"A significant number of them still need to be offered appointment dates."
'Clinic hours extended'
The report says there are 5,699 inpatients who need to be seen by the end of the year to meet the government's maximum six-month wait target, with 1,881 still without appointment dates.
A spokeswoman for Cambridge University Hospitals said: "We are on course to meet these targets. We have extended clinic opening hours and introduced additional clinic and operating theatre sessions."
On Monday a spokeswoman for Ipswich Hospital, which has about 2,000 outpatients needing to be treated by 31 December according to the report, said the hospital expected to meet the government waiting time targets.
A West Suffolk Hospital spokeswoman said: "There are a total of 2,222 patients currently waiting to see a consultant after being referred by a GP. All these patients are due to be seen within the 13-week waiting time target."