There has been little considered reflection by Catholic theologians on the concepts of gender identity, gender dysphoria and gender transition. Seeking inspiration in the Scriptures, some Catholic thinkers have interpreted the first three chapters of Genesis and especially the text ‘male and female he created them’ (Gen. 1:27) as requiring all human beings to live in the gender role congruent with their biological sex, and have viewed the biology of sex as self-evident. This article argues that these chapters constitute an appropriate locus for reflection on theological anthropology but that they need to be taken together with other texts and especially with the explicit teaching of Jesus Christ. In the Gospel according to Matthew, the one occasion in which Jesus invokes this passage from Genesis is when he draws attention to exceptional examples in nature and, in a striking phrase, states that some ‘have made themselves eunuchs for the sake of the kingdom of heaven’ (Matt. 19:12). If the Genesis text is interpreted in the light of the words of Christ, the binary division of the sexes, while ordained by God and the basis for a vocation to marry and procreate, admits of exceptions both natural and supernatural.