The NHS needs to “listen harder” to patient complaints, according to a report.
When people criticise the way their care was handled, health trusts too often give a poor or incomplete explanation, it said.
The study, from the health service ombudsman Ann Abraham, examined 15,579 complaints made about the NHS in England in 2009/10.
The ombudsman is the “next step” for patients dissatisfied with the response they get from an NHS trust.
Overall, more complaints were received about hospital, specialist and teaching trusts than any other group (6,304 complaints, or 44% of the total).
The figures are not comparable with last year due to changes in the way complaints are assessed.
Some 17% of complaints received (2,419) were about GPs - the second most complained about group.
Overall, 63% of all complaints investigated and reported on by the ombudsman were upheld or partly upheld.
Of complaints about GPs, 56% were upheld or partly upheld, while 80% of 659 complaints about dentists were upheld or partly upheld.
Ms Abraham said: “Many of the lessons that can be learnt from complaints are straightforward and cost little or nothing to implement at local level: a commitment to apologising when things go wrong; clear and prompt explanations of what has happened; improved record keeping and better information for patients about how to complain.”
She said poor quality or inconsistent information about complaints “diminishes learning within the NHS and impedes access to choice for patients”.
Health minister Simon Burns said: “I welcome this report which highlights that the NHS needs to take patient complaints more seriously and manage them more efficiently locally, rather than simply relying on the health service ombudsman.
“Through our information revolution, which we are consulting on right now, we want to make sure patients have the information they need to help them make meaningful decisions about their care.
“Patient feedback and complaints are an important source of information - and the experience of other sectors clearly shows that strong user feedback can have a positive impact on services.”