Smoking is well known as a risk factor for type 2 diabetes, but scientists say quitting the habit can raise the risk even more in the short term.
A study by US researchers found that people who stop smoking have a 70% increased risk of developing type 2 diabetes in the first six years without cigarettes as compared to people who never smoked.
The researchers say they suspect the increased diabetes risk comes from extra weight gain common in people who quit.
But they say no one should use their findings as an excuse to continue smoking - a habit which can also cause lung disease, heart disease, strokes and many types of cancer.
"The message is: Don't even start to smoke," says Hsin-Chieh Yeh of the Johns Hopkins University School of Medicine in the United States, who led the study.
"If you smoke, give it up. That's the right thing to do. But people have to also watch their weight."
Type 2 diabetes - often called adult-onset diabetes - is a common disease that interferes with the body's ability to properly use sugar and insulin, a substance produced by the pancreas which normally lowers blood sugar after eating.
Overweight people and those with a family history of the disease have an increased risk of developing it, as do smokers.
Diabetes is reaching epidemic levels, with an estimated 180 million people suffering from it around the world.
Yeh's study, published in the Annals of Internal Medicine journal, looked at almost 11,000 middle-aged adults who did not yet have diabetes from 1987 to 1989.
The patients were followed for up to 17 years and data about diabetes status, glucose levels, weight and more were collected at regular intervals.
The researchers found that people who quit smoking had a 70% increased risk of developing type 2 diabetes in the first six years after stopping compared to people who never smoked.
The risks were highest in the first three years, and returned to normal after 10 years.
Among those who did not stop smoking the risk was lower, but the chance of developing diabetes was still 30% higher compared with those who never smoked.
Tobacco is the leading preventable cause of death in the world, killing more than 5 million people a year.
A report by the World Lung Foundation last August said smoking could kill a billion people this century if trends hold.
