Along with adding scores of "custom gender" options on profile pages, Facebook is letting members select which pronouns they wish used when referring to them in posts or messages.
Along with "he/him" and "she/her" options, there is a neutral "they/their" choice.
"While to many, this change may not mean much, for those it affects, it means a great deal," Facebook said in a post at its Diversity page that included a picture of a rainbow flag on display on the company's campus in the Silicon Valley city of Menlo Park.
"We see this as one more way we can make Facebook a place where people can express their authentic identity."
Facebook said it worked with lesbian, gay, bisexual and transgender activist groups to create a thorough list of gender options, which can be found in an "other" category on profile About pages.
Custom genders are only available to those who use Facebook in US English, but the company plans to expand the range in the future.