A new ad campaign to tackle the obesity problem in the region was launched by the Public Health Agency (PHA) on Thursday.
It comes after the latest Northern Ireland Health Survey showed 61% of adults in Northern Ireland are overweight or obese.
However 43% of those assessed as overweight felt their weight was about right or too light, showing individual perceptions are often wrong.
Chief Medical Officer Dr Michael McBride says tackling obesity is "one of the biggest public health challenges" in Northern Ireland.
"Obesity is a modern lifestyle epidemic that is threatening our health and wellbeing," he said.
As part of the campaign, the PHA is encouraging people to measure their waist to identify whether they are overweight or obese.
Run a tape measure around your waist just below your belly button and if you're over 32 inches for women and 37 inches for men, it's a sign that you may need to take some steps.
Dr Carolyn Harper
"More than one in two adults in Northern Ireland are now overweight or obese, but many people don't even realise that they fall into this category and are putting their health at risk," Dr Carolyn Harper, Director of Public Health, said.
The PHA says being overweight or obese increases the risk of developing heart disease, some cancers and type 2 diabetes.
A website, called Choose To Live Better, provides helpful tips and practical advice on how people can measure their waist and reduce their weight.
"We want people to think about whether they are inching towards poor health and to take positive action to address it if they are," Dr Harper said.
"This campaign aims to help people recognise when they are overweight or obese, explain the health effects, and encourage those who need to, to make small, realistic lifestyle changes that will help them maintain a healthy weight."
The campaign will initially run until the end of March 2013.