In all, 245 clinical management events were recorded, up from 205 in the 2014-2015 year.
They included 56 delays in diagnosis or treatment where an issue in the referral process led to a delay in seeing a specialist. The key clinical issue was not discovered at the first assessment in 32 patients.
A further 26 patients were affected by under-resourcing such as not enough equipment or staff to meet demand.
There were pressure injuries caused when staff did not change the position of bed-bound patients, inadequate monitoring of breathing rates following the use of morphine, patients' deterioration not realised quickly enough, incomplete coordination of care, security issues, allergic reactions and transfer problems.
Also recorded were 44 events related to ophthalmology, including delays in people getting follow-up appointments to see ophthalmologists, and in some cases eye conditions deteriorated.
The clinical mistakes made up 47 per cent of the serious adverse events recorded by district health boards across the country in the 2015-2016 year.
Injuries from falls dropped from 53 per cent last year to 46 per cent this year, or 237 falls, 84 of which resulted in a broken femur.
Other falls resulted in broken hips.
Labour health spokeswoman Annette King said the report made grim reading and reinforced claims from ophthalmologists that waiting lists for eye treatment were too long.
"They claim that meeting waiting time targets means that there is not enough resources to do follow-up appointments.
"The Commission says this means that some New Zealanders are suffering a serious degradation of their sight."
King said the mistakes and delays were caused by an under-funded health system.
Commission chairman Professor Alan Merry said though the number of adverse events had increased from 182 in 2007 when reporting first began to 520 this year, this reflected a "progressive increase in our culture of transparency and commitment to learning from things that go wrong in health care".
Merry said falls had reduced 14 per cent because of support provided by a reducing harm from falls programme, and efforts across the sector to reduce the risk of falling and risk of sustaining serious harm.
The improvement had been achieved through the commitment of DHB staff working with patients and their families to assess risk and implement prevention strategies, he said.
No clinical mistakes were reported relating to blood or blood products, nutrition, oxygen, gas or vapour, or infrastructure.
Outside of public hospitals there were 154 adverse events to patients by other providers such as private hospitals and ambulance services.
Mental health adverse events were recorded separately and a report into the 185 events would be released later this year through the Office of the Director of Mental Health.
Serious adverse events in 2015-16:
• 520 adverse events (525 in 2014-15) and 154 by other providers
• 245 clinical management events (47 per cent), including 12 deaths
• 237 serious harm incidents from falls (46 percent). Of these, 84 resulted in a broken femur
• 21 medication-related events (4 per cent).
