GPs have been over-paid millions of pounds for patients who have moved practice, died or been forced to leave the country, according to a new report.
A one-year review by the Audit Commission identified more than 95,000 patients who needed removing from GP lists in England and Wales.
They included almost 30,000 patients who had moved to another practice (31% of the total), more than 32,000 who had died years before (34%) and almost 10,000 failed asylum seekers (10%).
Nearly 20,000 patients (21%) were also removed from lists after investigators found high numbers of people registered at the same property.
While it would not be unusual for 50 patients to be registered at a nursing home, 20 patients registered in one house would suggest inaccurate GP lists, the Commission said.
Of those patients who had died but were still on GP lists at the time of the review in 2009/10, 157 died before 1980 including one patient whose GP continued to be paid for their care for around 40 years despite the fact they died in 1969.
A further 335 patients had been on lists for up to 30 years despite dying between 1980 and 1990, while another 429 had died between 1990 and 2000.
Inaccurate GP lists can mean some practices receive more than their fair share of funding, while others miss out.
When patients move to another practice, failing to remove them from an existing list can also mean two GPs being paid for one patient's care.
GP practices are paid £64.59 for each patient on their list. Today's report said the removal of more than 95,000 "ghost patients" meant the NHS had been able to save more than £6.1m in one year.
Following the review - known as the National Duplicate Registration Initiative (NDRI) exercise - the medical records of almost 30,000 patients were transferred from patients' former GP to their current one.
It is the job of primary care trusts (PCTs) in England and local health boards in Wales to keep an up-to-date list of patients.
Overall, the 95,000 patients represent around 0.16% of the population.
Andy McKeon, managing director of health at the Audit Commission, said: "The NHS and GPs generally manage patient lists well - at any one time there are some 58 million records and many movements on and off lists.
"However, the NDRI, and active follow-up locally of duplicates and other anomalies, has resulted in £6.1m annual savings.
"It is disappointing that some areas did not rigorously follow-up the information provided by NDRI, which would have resulted in more savings."
The NDRI compares GPs' patient lists with those of other GPs and with other lists to find 'matches'.
These identify a duplication or anomaly in the data which need further investigation.
Dr Laurence Buckman, chairman of the British Medical Association's GPs Committee, said: "We are glad that the Audit Commission recognises that the NHS and GPs generally manage patient lists well bearing in mind the number of records held and the amount of movement of patients in and out of practice areas.
"It is important that lists are as accurate as they can be and 'ghost patients' should be routinely picked up by primary care organisations (PCOs) and removed as a matter of course.
"However, we have been concerned by reports from some areas of over-zealous list cleaning initiatives, where patients still validly registered with a practice have been removed against theirs and their GP's wishes, often without their knowledge.
"Often these are vulnerable patients - either elderly or non English speakers.
"It is important for PCOs and practices to work together to make sure that ghost patients are correctly identified and genuine patients are not disadvantaged."
Health minister Lord Howe said: "Although 52.5m people live in England, 55 million people are registered with a GP.
"Identifying 'ghost patients' will ensure that practices are fairly funded only for the patients they are responsible for.
"The NHS needs to make the best use of the funds it has available and avoid giving GPs extra income for patients who have moved away or died."