A leading charity is warning the NHS in Wales could be overwhelmed by diabetes.
Diabetes UK Cymru said that with hundreds of thousands of people at increased risk of developing the condition, turning the tide was a major test for devolution.
Some 167,000 people are being treated for the disease in Wales, a 9.4% increase in two years.
The Welsh government says it wants diabetes care to be comparable to the best in Europe.
A new diabetes action is due to be in place by June.
Dai Williams, director of Diabetes UK Cymru, told Sunday Politics that turning the tide is a major test for Welsh ministers and devolution.
This is because 350,000 people have higher than normal blood glucose levels - and a much increased risk of developing the disorder.
Diabetes can deprive people of their eyesight and cause strokes, kidney failure and premature death.
The increase is blamed on more people becoming overweight and not getting enough exercise.
In the past week north, mid and west Wales had the first glimpse of how Wales' local health boards plan to reshape services.
They must try to convince sceptical, often angry, communities they are doing the right thing.
Yet within those communities diabetes is threatening to spiral out of control.
Eirian Jones, from Pencader in Carmarthenshire, was diagnosed with type two diabetes two years ago, after a routine blood test.
"I've been quite fortunate where I believe I was diagnosed very early on in my diabetes so I am less susceptible to the complications," she said.
"But you imagine somebody walking around for maybe ten years having the disease and not knowing it.
"By the time they discover they are diabetic, the damage is done."
In just two years the number of people being treated for diabetes in Wales has increased by 9.4% to around 167,000.
That figure is on course to pass a quarter of a million by 2025.
"Waiting in the wings we've got 350,000 people with what's called pre-diabetes, so their chance of developing the diabetes is much higher," said Mr Williams.
"The result of that for Wales, effectively, is it's costing the NHS half a billion pounds a year.
"So we should be very worried about it."
He said politicians had a plan to deal with it but it must be "implemented and followed through".
There are also concerns about the lack of medical staff to treat and educate patients about diabetes.
Tina Donnelly, director of the Royal College of Nursing in Wales, said: "I do feel that there's insufficient resources put into the role of specialist practitioners.
"I am talking about clinicians across the board, but I would say about nursing staff there are insufficient specialist nurses in Wales who are trained in the care of diabetes to deal with the numbers of population who are suffering."
The assembly's health committee is holding an inquiry into diabetes services as ministers consult on a new diabetes action plan.
The Welsh government told Sunday Politics it aims to have diabetes incident rates and health care outcomes comparable to the best in Europe.
"Consultation on a diabetes delivery plan for Wales is under way," it said in a statement.
"The draft plan states what the Welsh government expects of the NHS, starting with the local health boards having effective plans in place by June 2013 to prevent diabetes and reduce the risk of long-term diabetic complications.
"As well as providing care and treatment for people with diabetes, we are continuing to invest to raise awareness of the importance of a healthy lifestyle including a healthy diet, drinking alcohol sensibly and not smoking, through creating environments that help people to make healthy choices."