Norfolk and Suffolk NHS Foundation Trust failed to act on 258 recommendations
A mental health trust failed to act on 258 recommendations from 98 reviews into serious incidents, such as patient deaths, a report has revealed.
The report to Norfolk and Suffolk NHS Foundation's Trust's board said there was a "risk" in having outstanding recommendations.
Former Norfolk coroner William Armstrong said the trust's failure to act was a "serious concern".
The trust said staff were receiving additional training.
Serious incident reviews take place after there are unexpected or avoidable deaths or severe harm to a patients, or allegations of abuse.
Last week the trust became the first of its kind in England to be put in special measures.
The report to its board said recent Care Quality Commission (CQC) reports on the trust said "learning at all levels of the organisation is not taking place".
Mr Armstrong, who is also chairman of watchdog Healthwatch Norfolk, said as Norfolk coroner he had seen a number of cases of deaths of mental health patients where serious incident inquiries had been conducted by the trust.
"It would be a serious concern if recommendations in a report make a commitment to learn lessons to reduce risks... and they are not implemented," he said.
Some of the recommendations from the reviews date back to 2012.
Vicki Nash, head of policy and campaigns at Mind, said: "Serious incident reviews are an essential part of the process of understanding how incidents including deaths, severe harm and abuse have occurred and what, if anything, could have been done to prevent them.
"Any recommendations that come out of them have to be taken seriously and implemented swiftly to ensure that healthcare providers learn from past mistakes."
Emma Corlett, who represents Unison members at the trust, said: "It is a surprise to see that level of recommendations still to be implemented. Our staff will be really concerned about that."
A spokesman for the Campaign to Save Mental Health Services in Norfolk and Suffolk said: "It is deeply shocking and insulting to patients and their families that the trust has failed to implement 258 recommendations, despite repeatedly promising 'lessons will be learnt'."
Jane Sayer, director of nursing at the trust, said that while some recommendations could be put in place immediately, "others will take a while to roll out".
She said: "Four hundred and fifty improvement actions, resulting from serious incident reviews recommendations, have been carried out in the past year alone.
"We are not complacent about this issue... and we now offer additional training and support to frontline staff to encourage them to not only implement the actions but to fully report back."