Pancreatic cancer is often diagnosed at a late stage
Obese women, who carry most of their excess weight around the stomach, are 70% more likely to develop pancreatic cancer, research suggests.
Obesity was thought to increase the risk - but more in men than women.
However, the new study, of more than 138,000 postmenopausal US women over seven years, suggests it is a significant risk factor for women too.
The study, by Sweden's Karolinska Institute, appears in the British Journal of Cancer.
In total 251 women in the study developed pancreatic cancer.
After taking account of other risk factors such as smoking, the researchers calculated that the disease was 70% more likely in women with the highest waist-to-hip ratios - a measure of obesity.
Lead researcher Dr Juhua Luo said: "We found that the risk of developing pancreatic cancer was significantly raised in obese postmenopausal women who carry most of their excess weight around the stomach."
Pancreatic cancer is the UK's sixth most common cause of cancer death.
In 2004, around 7,400 cases of pancreatic cancer were diagnosed in the UK, and there are around 7,000 deaths from the disease each year.
Usually, the disease is diagnosed only once it has spread and is difficult to treat successfully.
Only 2-3% of people survive beyond five years after being diagnosed.
The researchers believe obesity may increase the risk of pancreatic cancer by affecting insulin levels.
Dr Luo said: "We know that carrying a high proportion of abdominal fat is associated with increased levels of insulin, so we think this may cause the link between obesity and pancreatic cancer."
Dr Lesley Walker, of the charity Cancer Research UK, said: "Pancreatic cancer is associated with particularly poor survival, so it is crucial that we learn more about how to prevent the disease.
"About a quarter of all cancer deaths are caused by unhealthy diets and obesity and it's important that people are aware of this risk."
Lucie Galice, of World Cancer Research Fund, said: "Looking at all the studies that have been done on this subject, overall there is convincing evidence that excess body fat increases risk of pancreatic cancer.
"There is also convincing evidence that being overweight increases risk of post-menopausal breast cancer, bowel cancer and cancers of the kidney, oesophagus and endometrium.
"In fact, scientists now say that, after not smoking, maintaining a healthy weight is the most important thing you can do for cancer prevention."
Pancreatic cancer develops from the cells within the pancreas, a gland located high up in the abdomen just behind the stomach.
If pancreatic cancer is not treated, cancer cells can spread into nearby organs or lymph nodes, or, eventually, break away and spread to other parts of the body.