Men over the age of 50 are almost twice as likely as women to have diabetes without knowing it, it was claimed.
A study of more than 6,700 UK adults aged 52 to 79 found that 502 had type 2 diabetes, the most common form of the disease.
Of the affected men, 22% did not previously realise they had the condition compared with 12% of the women.
Type 2 diabetes is linked to lifestyle and associated with having a large waist or being overweight.
Study leader Dr Mary Pierce, from University College London, said: "The higher numbers of men with undiagnosed diabetes in this study may be explained by the fact that women go to their GP more often and are therefore screened more often.
"There needs to be much greater testing of overweight and obese people as well as those with other risk factors for diabetes."
Around two million people in the UK have type 2 diabetes. A further 750,000 are believed to have the disease without knowing it.
The new research was reported in the journal Diabetic Medicine.
It found that people had a greater risk of having undiagnosed diabetes if they had a high Body Mass Index (BMI), a measurement of weight related to height, a large waist, high blood pressure and high cholesterol.
Wealth, education, social class, ethnicity, age and smoking status were not significantly associated with increased risk.
