Margaret "Margot" Pegum, 68, had the surgery in April 2015 to help her lose weight but within three months - following another operation to increase the size of the balloon - she died of sepsis caused by a hole in her stomach.

Deputy State Coroner Elizabeth Ryan on Thursday found there was no evidence to support a doctor's assessment the procedure was safe or appropriate for Ms Pegum given she'd undergone earlier gastrointestinal surgery.

"No peer-reviewed literature or guidelines supported his conclusion that it was safe to proceed," Ms Ryan said at Glebe Coroner's Court.

Ms Pegum should have been told a previous procedure she had in 2012 - to treat severe acid reflux - meant her later surgery by Dr George Marinos wasn't a good idea.

That was the advice in peer-reviewed research and also from the gastric balloon manufacturer, the coroner found.

Dr Marinos admitted during the inquest he had not informed his patient of that and accepted his decision to proceed with the surgery was "unwise".

Ms Pegum had also received "deficient" care and advice after her balloon was further inflated in June 2015 - including unclear instructions as to when to contact Dr Marinos if she experienced severe vomiting.

She began vomiting and dry retching soon after the operation. Abdominal cramps led her son, James, to take her to the Prince of Wales Hospital where doctors discovered a five-centimetre hole in her stomach.

Her condition deteriorated and Margot Pegum died on July 6.

James Pegum told reporters on Thursday his mother - who he described as fun, intelligent and generous - should never have had the procedure.

The findings were a "wake up call" that steps must be taken to prevent the industry experiencing the regulatory challenges the cosmetic industry had already faced, he said.

"The cosmetic industry went through this, with very few guidelines on how practitioners should work," Mr Pegum said.

"The bariatric industry is driving along the same road. We can't let it make the same mistakes.

"It's incumbent on every health department across the country to ensure that that does not happen."

The coroner has recommended the Australian and New Zealand Metabolic and Obesity Surgery Society develop guidelines for gastric balloon surgery and consider creating a data registry listing patients and their outcomes.

Dr Marinos has made a range of changes at his surgery since Ms Pegum's death including not performing gastric balloon operations on those who have had a fundoplication, the earlier gastrointestinal procedure Ms Pegum had.

Australian Associated Press