There has been a five-fold increase in the number of people committing suicide while patients in public hospitals.
A report by the Health Quality and Safety Commission on serious and sentinel events issued on Wednesday said there were 360 cases of harm to patients over the year ending in July.
Ninety one patients died - slightly more than the year before - but not necessarily as a result of the error or incident.
The main cause of harm was falls, which decreased, while there were 17 suspected inpatient suicides - up from three - and a rise in cases of delayed treatment because of hospital system failures.
The commission said suicides can be extremely hard to prevent and there appeared to be no common factors involved.
Suicides will be covered later in a separate report, but the commission says it was just a bad year for in-patient suicides, half of which occurred away from hospitals, and it doesn't expect so many next year.
But the Mental Health Foundation is urging healthcare providers to strive for a seamless transition for mental health patients leaving hospital.
Foundation chief executive Judi Clements says improvements may be needed.
And the commission is urging doctors to follow up when they have ordered tests, to ensure patients get treated quickly.
Commission chair Professor Alan Merry says that he is worried about a growing number of delays in the treatment of patients.
These are largely because modern health systems are more complex than they used to be, he says.