A inquest jury has returned a verdict of death by natural causes aggravated by neglect on 10-year-old Robbie Powell who died in 1990.
Robbie Powell, from Ystradgynlais in south west Wales, died from Addison's Disease, a rare but treatable condition which affects the adrenal glands.
His parents had spent years campaigning for an inquest, and now want a public inquiry.
The inquest heard how Robbie had been seen by a succession of doctors, but none had diagnosed the condition.
His symptoms of sickness and stomach pain were thought to be gastroenteritis.
First Minister Rhodri Morgan, who has met Robbie's parents, said the Welsh Assembly Government had received daily transcripts of the inquest.
Mr Morgan said a "huge mass" of evidence had to be studied, but added: "I am sure that there are lessons to be learned from the evidence in this tragic case."
The General Medical Council said: "We are aware of concerns about a number of doctors relating to this case.
"We will be studying the judgement made at the inquest in relation to these concerns, to see what action, if any, may be appropriate."
Speaking after the inquest in Swansea, Robbie's parents said they were disappointed at the verdict and would continue their campaign.
"I am not happy with the verdict," said William Powell. "I wanted unlawful killing.
"It's not a criticism at all of the jury, the evidence was restricted in this court."
Mr Powell added: "Had these doctors... apologised for their failures and maybe shed a tear for Robbie and had some regard for his life, my wife and I would have felt that was punishment enough."
"I promised him on his death bed that I'd try to establish the truth.
"I believe that I've partly fulfilled that promise - it's the system that's failed us and Robbie and I'll still battle on."
William Powell has fought for the truth to be heard
The inquest had heard that in December 1989 Robbie had been seen by a consultant paediatrician who had suspected Addison's Disease, but made a "gross mistake" by not ensuring that a test was carried out to detect the condition.
Robbie's symptoms were treated, and he was discharged from hospital.
Four months later, he became ill again, and within a period of two weeks was seen seven times by five family doctors - none of whom took action which would have saved his life.
On the day he died, on 17 April 1990, Dr Nicola Flower, who had been a GP for eight months, was called to the Powell's home because Robbie's condition was deteriorating.
She did not believe he was ill enough to go to hospital but two hours later, she wrote a referral letter.
Robbie's father, William told the inquest that Dr Flower had refused to call an ambulance and there had been an argument.
In the inquest, Kieran Coonan QC suggested that had only been a discussion.
It was Mr Powell who took his son to Morriston Hospital, in Swansea, where he died within hours of a heart attack.
After the post mortem, Mr and Mrs Powell discovered their son had died of Addison's Disease.
They acquired Robbie's medical files and embarked on a long campaign to find out what had gone wrong.
There were three police investigations; a civil court case; a Welsh Office inquiry; a health authority review and an ombudsman's ruling.
But all the hearings were held in private, and the family wanted an inquest.
That inquest ended on Friday, and afterwards, a solicitor for the doctors said they were extremely saddened by Robbie's death but felt that the jury had, to a degree, vindicated them by not saying it was not due to their personal neglect that Robbie had died.
Swansea NHS trust also recognised the family's distress and added that there had been many improvements in their procedures since Robbie's death.
The trust pointed out that in May 1996 the former West Glamorgan Health Authority "accepted that Robbie did not receive the optimum level of care at Morriston Hospital in January 1990" and it had accepted civil liability.
"In so doing, the authority considered that no individual clinician was to blame," the trust added.