More than 400 people in the isles are believed to suffer from diabetes without having been diagnosed.
Government figures show a worrying number of people are at “significant risk” of developing health issues and complications from the condition.
The findings, obtained by Highlands and Islands Labour MSP David Stewart through a series of parliamentary questions, show 1,024 people in Shetland have been diagnosed with the life-changing condition. But an estimated 416 people still have not been diagnosed.
Mr Stewart sits on the cross-party group in the Scottish Parliament on diabetes as co-convener. He was appointed the Scottish Parliamentary champion for diabetes last year and has now called on the Scottish government to develop a diabetes action plan.
He said: “The numbers of people living with undiagnosed diabetes in Shetland is simply staggering, and could easily be rectified.
“I have been calling on the Scottish government to take steps towards finding the undiagnosed through high risk screening for type 2 diabetes.
“We know who the at risk groups are and therefore who the Scottish government need to target, those who are overweight, those who are over 45 and those with a family history of the condition.
“These figures show that the Scottish government need to review the Scottish diabetes action plan and develop a proactive agenda for the future.
“Scotland has one of the highest incidences of type 2 diabetes in the world; it’s obvious that we should be screening those at risk before it ends in emergency.
“Diabetes remains the main cause of blindness in people of working age and the main contributor to kidney failure, amputations and cardiovascular disease.”
Rupert Pigot from Diabetes Scotland said: “These figures show the extent of diabetes in the Highlands and Islands, and that it is increasing. Being able to diagnose Type 2 diabetes early means that people will receive the proper care and advice that means they can avoid the serious complications associated with diabetes.
Addressing the amount of undiagnosed cases in Scotland has no easy answers, there must be a strong co-ordination of NHS Scotland and Scottish government to examine methods to identify people at high risk of diabetes and ensure that they avoid further problems.”