Jolie wrote that her mother fought cancer for nearly a decade and died at the age of 56. With six kids of her own in mind, Jolie decided to get a blood test done.
The 37-year-old actress learned that she carried the faulty BRCA1 gene that would sharply increase her own risk of developing breast cancer by 87 percent and ovarian cancer by 50 percent. Her odds are now 5 percent.
Jolie said knowing the medical reality helped her be proactive. The medical procedures, including surgery, began in February and finished with reconstruction of the breasts with an implant in late April. She had her surgeries at Pink Lotus Breast Center in Beverly Hills.
"I choose not to keep my story private because there are many women who do not know that they might be living under the shadow of cancer," Jolie wrote. "It is my hope that they, too, will be able to get gene tested, and that if they have a high risk they, too, will know that they have strong options. Life comes with many challenges. The ones that should not scare us are the ones we can take on and take control of."
Jolie said her partner, actor Brad Pitt, was by her side every step of the way.
Jolie is also getting support from other celebrities, including E! News host Giuliana Rancic, who had a double mastectomy after being diagnosed with breast cancer.
"Angelina Jolie reveals double mastectomy. Proud of her for using her incredible platform to educate women," Rancic tweeted.
Singer Sheryl Crow, who is also a breast cancer survivor, commended Jolie.
I commend Angelina Jolie for her courage and thoughtfulness in sharing her story today regarding her mastectomy. So brave!" Crow tweeted.
