The confidential records of more than 3,000 patients were mistakenly dumped in landfill, it has emerged.
The records should have been shredded or burned
Bolton Primary Care Trust (PCT) has written to about 3,200 patients after paper notes detailing their care were dumped rather than shredded or burned.
A statement from the trust said all patients had been contacted about the matter and it has provided information lines for anyone worried.
Roger Goss, from Patient Concern, said it was a "ridiculous" error.
"We are all told that we should shred our important records and documents to protect our personal identity, so how the heck does a hospital not realise that it has a responsibility to do this?," he said.
The PCT's chief executive, Tim Evans, said it was "sincerely sorry".
A statement from the trust said the patients affected had either attended the anticoagulant (anti-blood clotting) clinic at the Waters Meeting Health Centre between September 2007 and January 2008, or received a visit from the out-of-hours GP services between December 2007 and January 2008.
The statement read: "As soon as the problem was discovered actions were put in place to prevent a repeat of the mistake.
"The records that were disposed of were copies of information that had been routinely transferred to computer.
"There is no adverse impact on the care and treatment of patients."
A spokesman for NHS Connecting for Health, which is overseeing the creation of electronic patient records, said: "After any data loss such as this, sensitivity about the storage of medical records is understandably an issue.
He added: "The old paper system cannot properly service a 21st Century healthcare system.
"That is why NHS Connecting for Health is putting in place an electronic summary care records system with security controls that meet the strongest national and international standards.
"The level of security is higher than in internet banking. There will be no need for paper records and any risk to confidentiality attached."