Jewish communities have always had children with intersex conditions, which involve atypical anatomic, chromosomal, or gonadal sex. In the last several decades, Orthodox rabbis have issued ad hoc rulings to assign sex to children and adults with intersex conditions. However, rabbinic texts reflect disunity over whether to assign gender, for the purposes of Jewish law, according to outward appearance or chromosomal makeup. This rabbinic controversy has been exacerbated by an increasingly complicated medical picture. Endocrinologists have diagnosed more than two dozen intersex conditions, across nine overarching congenital types. Such complexity makes it difficult for rabbis to make across-the-board decisions about gender assignment. This essay examines how rabbinic law may change because gender cannot be assigned consistently by chromosomal sex—despite the prevalence of this formulaic criterion in rabbinic opinions. Consequently, Jewish legal reasoning is poised to shift from a static reliance on chromosomal sex. The essay also considers the implications of this trajectory on Jewish law towards sex change surgery and transsexuals.