An elderly woman died in Tauranga Hospital after doctors failed to act on a suggestion made by her family doctor.
The case in mid-2010 is detailed in findings released on Monday by Health and Disability Commissioner Anthony Hill.
Mr Hill said the generally healthy 78-year-old was referred to hospital because of vomiting, coughing and a lump that her GP suspected was a hernia.
This was spelt out to hospital staff, but the unnamed junior medical registrar who admitted the woman failed to pass it on to the unnamed senior doctor.
The second doctor was under extreme time pressure and decided that the lump might be cancerous, but failed to consider a hernia as a possible diagnosis.
The hernia was discovered after the woman deteriorated, suffering a heart attack and a fatal brain injury.
Anthony Hill said the senior doctor, the registrar and the Bay of Plenty District Health Board breached patient rights.
The commissioner told Radio New Zealand's Checkpoint programme on Monday the GP's notes should not have been ignored and doctors at the hospital acted inappropriately. He said he would check in July on what changes have been made.
Bay of Plenty DHB chief executive Phil Cammish said the mistakes were isolated incidents and it has dealt with and learned from them.
Mr Cammish said training of registrars and others had also improved.