Diabetes is caused when the body lacks insulin and cannot convert sugar
It is estimated that 50,000 people living in Wales have diabetes but are unaware of it, according to a charity.
To highlight its message, Diabetes UK Cymru is visiting five locations to raise awareness of the life-threatening complications the disease can produce.
Four other health charities are backing the initiative.
Members of the public are being offered free diabetes risk assessments by 700 pharmacies across Wales as part of the week-long awareness drive.
Around 140,000 people in Wales have diabetes
In June, research by the charity showed people living in deprived parts of Wales were twice as likely to have the condition as those in more affluent areas.
Public health experts said efforts to prevent and treat the disease should be targeted at the most vulnerable.
DIABETES BUS TOUR
Monday - Bangor, by the clock
Tuesday - Aberystwyth promenade
Wednesday - Carmarthen, Guild Hall Sq
Thursday - Neath, Angel Sq
Friday, Sunday - Barry seafront
The bus times will be between 1000-1400 daily
Dai Williams, National Director of Diabetes UK Cymru, said: "It's terrifying that there are around 50,000 people in Wales with diabetes who do not know it.
"People can live with the condition for up to 10 years without knowing it, which means many of them have the serious complications of diabetes by the time they are diagnosed.
"The week is the perfect opportunity for people to have a diabetes risk assessment at their local pharmacy and to visit the bus to find out more about the condition.
"We want to find the missing 50,000 to ensure they can manage their diabetes well and live longer, healthier lives without complications."
Over 40 people with diabetes are taken to hospital with heart attacks every week, 17 suffer strokes and five more have amputations every week in Wales.
There are two forms of diabetes, known as type 1 and type 2. Type 1 occurs in people who are unable to produce insulin and is usually diagnosed in childhood or early adulthood and treated with insulin injections.
Risk factors for type 2 diabetes, which tends to affect people as they get older, include being overweight, having a close relative with the condition, being aged over 40 or over 25 for people who are black, Asian or from other ethnic minorities.
This type can usually be controlled by diet and exercise, but if it progresses may need medication or insulin injections.
Some of the complications of diabetes include heart attacks, strokes, amputation, blindness and kidney disease.
The Stroke Association, the British Heart Foundation, Kidney Wales Foundation and RNIB Cymru are supporting the venture.