British researchers believe that iatrogenic ailments (unintended injuries, illnesses or symptoms induced in patients through a doctor's actions or words, or otherwise caused by adverse medical events) are responsible for thousands of deaths each year on wards, many of which are avoidable.
They include people being given the wrong treatment or drugs, or suffering falls. Only heart attacks and strokes kill more people each year.
The research, which will be based on existing American and Australian studies, is the first of its kind in Britain.
The doctors will try to measure these types of injuries, examine how much of an impact they are having on the National Health Service and work out what can be done about them.
Dr Maureen Dalziel, a specialist in public health issues who is involved in the project, said they expected the British study to find results similar to those of the previous foreign investigations.
"We expect it to be around the same level as the studies carried out in America and Australia because I've no reason to suspect the NHS doesn't provide the same quality of service," she said.
"I suppose we would hope that it will be less here than in the other studies, but assuming that you are living in a western society and expecting similar standards of care, it's unlikely there would be much of a difference."
The vast majority of adverse events affect patients who are undergoing surgery, mainly because they are likely to be already ill, and more susceptible to further infection.
Dr Dalziel said: "Fifty per cent of these adverse events are associated with operations followed by diagnostic errors, then treatment errors, drug errors, and then things like the patient falling, although things like falls are minor factors."
She said that on top of the deaths caused by adverse events there are many other factors that increase the financial burden on the NHS. As most of the injuries occur in surgery, this usually leads to complications, possibly requiring more surgery or meaning the patient takes longer to recuperate, both of which increase costs, especially in terms of bed days lost.
The Australian study suggested that each adverse event could lead to a loss of 7.1 bed days. For a region such as North Thames, where the average cost per bed day is pounds 210, this means a cost of pounds 62.3m.
"We did look at the NHS as a whole and thought the total costs would be about pounds 1bn overall," added Dr Dalziel.
But the problem has gone largely unnoticed, with attention spread elsewhere.
"I think to date the concern has been managing financial resources rather than clinical, and making sure that trustees were not over-spending," she went on.
"Until recently this has been top of the managers' agenda. The focus has been on managers, and while the focus is on them there's been a nervousness about looking closely at anything else in case you find something you don't like."
In the American study, 3.4 per cent of all admissions to the hospital experienced some sort of adverse event, and of that 3.4 per cent a further 14 per cent resulted in death.
These figures were conservative compared to the Australian study, but when applied to hospital admissions in England and Wales, the scale of deaths from these adverse events became clear. There were more than 46,000 deaths based on 9m admissions to hospitals in England and Wales in 1997.
In the North Thames region of the NHS, an extrapolation from the American study shows that of 50,000 admissions per year, 1,850 will result in an iatrogenic injury. Of those injuries 500 will involve negligence, and 259 will result in the death of a patient - a one-in-193 chance of unnecessary death. A further 130 patients will suffer an injury leading to a long- term disability.
The pilot study begins next month in six hospitals in the North Thames region, and will run for one year. The British scientists will use the American study as the basis for their own study looking at adverse events determined by case notes from the fields of obstetrics, trauma and orthopaedics, general medicine, and general surgery.Reuse content