Women who inherit either of two faulty BRCA genes were at much higher risk of developing breast and ovarian cancer than other women, and at younger ages.
Actress Angelina Jolie generated headlines last year when she had her healthy breasts removed to reduce her cancer risk.
The study just out was the largest yet to show the power of preventive ovarian surgery for those women.
The surgery not only lowered their chances of getting either ovarian or breast cancer, but it could also reduce women's risk of death before age 70 by 77%, Stuff.co.nz reported.
Ovarian cancer was particularly deadly, and there was no good way to detect it early like there was for breast cancer.
So for years, doctors have advised BRCA carriers to have their ovaries removed between the ages of 35 and 40, or when women were finished having children.
The new study suggested the surgery, called an oophorectomy, should be timed differently for the different genes.
For women who carried the higher-risk BRCA1, the chance of already having ovarian cancer rose from 1.5% at age 35 to 4% at age 40, lead researcher Dr Steven Narod of the University of Toronto, Canada, said. After that, the risk jumped to 14% by age 50.
The study is published in the Journal of Clinical Oncology.