A third "custom" gender option for people's profiles is an acknowledgement of the "complicated" sexual identities of some of its users, the social networking site said.
"When you come to Facebook to connect with the people, causes and organizations you care about, we want you to feel comfortable being your true, authentic self," Facebook said in a post on its Diversity page.
Facebook said it consulted leading lesbian, gay, bisexual and transgender advocacy organizations to decide what new optional gender categories to add.
"Facebook users from across the country have been asking for the ability to reflect their gender accurately, and today Facebook showed they have been listening," Allison Palmer, a former GLAAD vice president who worked on the project with Facebook, told ABC News.
Facebook said it has reworked its privacy settings to let users decide with whom they want to share their custom gender.