Three other incidents also resulted in patient deaths in the region.
A patient with meningitis was deemed ''unwell'' and sent home from the hospital emergency department.
When eventually admitted, the patient was unresponsive to treatment. An external review found ''individual performance and system issues'' were at fault for substandard care.
Another non-fatal case revealed a patient had received ''conflicting discharge information'' resulting in an infected wound after hip-joint replacement. Additional surgery was required to clean the wound.
Northland District Health Board chief executive Nick Chamberlain said all 11 incidents had been investigated.
"Our target is zero harm to all patients," he said.
Issues around falls, which were responsible for four incidents, were being addressed, he said.
"While it is impossible to avoid falls altogether, we continue to introduce interventions that will reduce the rate of falls."
Two of the falls occurred in district hospitals. The others were in Whangarei Hospital. All four involved elderly patients.
Nationally, 360 serious and sentinel adverse events were reported in the 2011/12 financial year, down from 370 a year earlier. Ninety-one resulted in patient deaths, compared to 86 in 2010/11.
Commission chairman Alan Merry stressed not all reported events were preventable, but many involved errors which should not have happened: "In some tragic cases, errors resulted in serious injury or death."
Falls continued to make up most serious and sentinel adverse events in hospitals - accounting for 47 per cent of all cases. However, nine patients had surgical instruments or swabs left in them, 10 underwent the wrong procedure or treatment and, as well, there
were 18 reported mistakes with patient medication.
A jump in clinical management errors, specifically those relating to treatment delays, was flagged as a concern.
Suspected suicide cases increased sharply, from three in 2010/11 to 17 in 2011/12.
Three more had occurred since the end of the reporting period.
