Researchers have found that almost half of all men with prostate cancer die from the disease.
A study by experts at King's College London analysed the records of just over 50,000 men with the disease over a 10-year period.
They found that rather than dying mainly from other illnesses during the course of their ordeal, as previously thought, 49% of deaths are attributed directly to the cancer.
Between 1997 and 2007 some 20,181 of the group died.
Prostate cancer is the second most common cancer in men after lung cancer. It usually affects older men and can be a slow-growing disease.
There are about 37,000 new cases in the UK each year and more than 10,000 men die from the cancer annually.
Throughout the course of the study some 12% of deaths were due to other cancers, 17% to heart disease, 8% from pneumonia and 13% from other causes.
The findings were presented at the National Cancer Intelligence Network (NCIN) conference in London.
Simon Chowdhury, author on the study and consultant oncologist at Guy's and St Thomas' Foundation Trust in London, said: "This confirms that prostate cancer is a major cause of morbidity and mortality for a large number of men and the importance of ongoing and future research into this area."