NHS trusts are putting people at risk by failing to implement a critical system of safety alerts, campaigners say.
Patient Safety Alerts are issued when potentially harmful situations are identified in healthcare organisations.
Charity Action against Medical Accidents said 63% of trusts in England have at least one overdue alert.
But the Department of Health said in the vast majority of cases trusts responded to alerts in good time.
AVMA asked all NHS trusts in England how many outstanding alerts they had.
The charity said there were 1,242 cases where trusts had failed to act on alerts, even after deadlines for the implementation of safer measures had passed.
These include warnings about procedures in surgery, the risk of overdoses, and using medical equipment properly.
Twenty-nine trusts said they had 10 or more overdue alerts. Some were years past the deadline for completion.
AVMA said this was despite a warning earlier in the year about overdue alerts.
"There can be no excuse for trusts continuing to put lives at unnecessary risk," said chief executive Peter Walsh
"There needs to be a much more robust system for regulation."
AVMA said that more than two years after the deadline, 67 trusts had not taken action on an alert advising healthcare workers about avoiding overdoses with injectable medicines.
Lisa Richards-Everton said the situation made her "despair". Her husband Paul died in March 2007 while he was being treated for cancer, after being given a massive overdose. Another patient died for the same reason, and a patient safety alert was issued as a result.
"Three years on, and yet there are still trusts that haven't complied," she said. "I don't think they quite understand the importance of this."
But the report's conclusions have been challenged by the National Patient Safety Agency (NPSA) which issues alerts.
It said it took some trusts longer than others to put them into action because of staffing levels, the size of some organisations, and the different ways they were run.
And a spokesman said: "Almost all NHS organisations have reported completion with the vast majority of alerts - completion is 94%."
He added: "We do feel that the report does misrepresent the hard work and professionalism by clinicians who have worked hard to make sustained changes or adjusted their working practices during these challenging times."
Earlier this year, the Department of Health wrote to NHS trusts reminding them of the importance of acting on Patient Safety Alerts. It said the vast majority had been carried out.
Health minister Anne Milton said: "Across the NHS there must be a culture of patient safety above all else. We expect all NHS trusts to comply, in order to minimise any risks in the future."
The Care Quality Commission is responsible for making sure trusts act on safety warnings. It said there were often good reasons behind delays.
"There has been a significant improvement in trusts reporting compliance," said regional director Ian Biggs. "If we find that patient safety has been put at risk we will take action."
The NPSA is one of the quangos being cut by the government. The new NHS commissioning board will take over responsibility for the alerts.
Patient Safety Alerts are also sent to healthcare organisations in Scotland, Wales and Northern Ireland, but information was not available on their levels of compliance.