Noel Virtue, a published novelist who no longer writes due to ill health, called an ambulance several weeks ago feeling "very ill".
The 63-year-old already has heart disease and type 2 diabetes.
Mr Virtue said he waited in a corridor on a trolley-bed for five and a-half hours, after hospital staff found he had a "dangerously high fever".
The department was not busy, so the wait surprised him, but there was "almost no staff" on the shift.
No-one tried to prevent him leaving about 3am, when he gave up waiting, but a male nurse helped him to leave through an exit that he was too weak to open.
The nurse seemed "more interested" in giving him a form to fill in.
"If I filled in the complaint form, he said enthusiastically, they might do something about the delays. I asked him if this was usual, and he said `yes, every night, night after night after night'."
Mr Virtue sought private medical treatment at the urging of his GP, and was diagnosed with a cancerous growth in his bowel.
Dunedin Hospital emergency department service manager Anne Abbott said an investigation into Mr Virtue's complaint revealed he spent nearly four hours waiting, not five and a-half.
Reviewing his notes, Ms Abbott said the priority level assigned to Mr Virtue was appropriate given his symptoms. Patients were constantly observed and reassessed throughout their wait.
"It is particularly concerning that Mr Virtue made the decision to leave without any examination, as this type of decision can often carry considerable risk for patients."
She was pleased he had then received help through his GP.
While the department may have appeared quiet, records showed a large number of patients had been assigned a high priority because of the severity of their complaint, she said.
Immediate care was always given to the most sick and unstable patients.
She said the male nurse who handed Mr Virtue a complaint form took note of his departure, and reported that Mr Virtue advised him he felt better.
"We do acknowledge the fact that increasing numbers of patients presenting to the department and the resulting high workloads our nursing staff are having to carry in situations such as this can result in long waiting times and poor communication," Ms Abbott said.
Ms Abbott acknowledged the department was "small", and said various initiatives were under way to make it more efficient.
Mr Virtue, when contacted this week, said he was concerned the hospital appeared to be implying he had lied about his experience.
To get into the "system" he had to seek a private appointment, which was unacceptable, he said.
