Almost 1,000 patients are dying needlessly in hospitals every month due to errors in care, research has suggested.
Each year there are 11,859 preventable deaths in hospitals in England, the study found.
The deaths occurred because of poor monitoring of the patient's condition, wrong diagnosis or errors in medication or fluid replacement.
The research was published after a coroner launched a scathing attack medical staff who let a patient die of dehydration in a hospital bed.
Staff at St George's Hospital in Tooting, south London, did not give Kane Gorny vital medication to help him retain fluids, Westminster Coroner's Court heard. The 22-year-old even phoned police from his hospital bed as he was so desperate for a glass of water, the inquest was told. Deputy Coroner Dr Shirley Radcliffe told the hearing that "a cascade of individual failures has led to an incredibly tragic outcome".
The new research analysed data concerning 1,000 adults who died in 2009 in 10 hospitals in England.
The authors found that 5.2% of the deaths had a 50% or greater chance of being preventable - this percentage equates to 11,859 deaths in English hospitals each year, they said. Although the figures are still substantial, they are much lower than previous estimates, say the authors.
The study, published in BMJ Quality and Safety, found that 60% of the preventable deaths occurred in elderly, frail patients, with less than a year to live.
Lead researcher Dr Helen Hogan, of the London School of Hygiene and Tropical Medicine, said: "While any patient dying from an adverse event is a tragedy and any deaths in hospital due to poor care are of considerable concern, it is important that our estimate of the size and impact of the problem is accurate and we understand what we can do to prevent such incidents."
A Department of Health spokeswoman said: "Patients have a right to expect the very best care from the NHS. Any preventable death in hospital is unacceptable and we expect the NHS to ensure patients receive high quality, safe and effective care. We know that data like this can help hospitals to improve services."