Intersex people are those born with any of several sex characteristics, including chromosome patterns, gonads, or genitals that, according to the Office of the United Nations High Commissioner for Human Rights, "do not fit typical binary notions of male or female bodies". The opposite of intersex is endosex, which describes persons born with sex characteristics that are seen as typically male or female at birth.
Sex assignment at birth usually aligns with a child's external genitalia. The number of births with ambiguous genitals is in the range of 1:4,500–1:2,000 (0.02%–0.05%). Other conditions involve the development of atypical chromosomes, gonads, or hormones. The portion of the population that is intersex has been reported differently depending on which definition of intersex is used and which conditions are included. Estimates often range from 0.018% (one in 5,500 births) to 1.7%. The difference centers on whether conditions in which chromosomal sex matches a phenotypic sex which is clearly identifiable as male or female, such as late onset congenital adrenal hyperplasia (1.5 percentage points) and Klinefelter syndrome, should be counted as intersex. Whether intersex or not, people may be assigned and raised as a girl or boy but then identify with another gender later in life, while most continue to identify with their assigned sex.