The largest ever study into diabetes and cardiovascular risk in Ireland has found as many as 24,000 people could have undiagnosed diabetes.
It found that 17% of people were found to have abnormal initial fasting blood sugar levels.
Men were found to be two to three times more likely than women to have abnormal blood sugar levels and undiagnosed diabetes.
Report author and Vhi Healthcare Medical Director Dr Bernadette Carr said: "The results of our research suggest that the rate of undiagnosed type 2 diabetes and pre-diabetes is higher in Ireland than in similar European countries such as Britain and Holland.
"They also demonstrate how important it is for individuals to understand and manage their own health risks.
"By making some very simple lifestyle changes, people can improve their outcomes, and in the case of pre-diabetes can even delay or prevent progression to diabetes."
The research found that people with abnormal blood sugar levels were significantly more likely to be older, male, smokers and have higher blood pressure.
It said they were also less likely to exercise five days a week or eat fruit or vegetables each day.