ABSTRACT The role of Sex reversal Y (gene symbols Sry for mice, SRY for humans) in gonadal phase sexual differentiation and maintenance is well established. Sex reversal Y is expressed in the preimplantation embryo, and some of the many genes differentially expressed by sex in such embryos do so because of it (with the majority controlled by the sex chromosomal ratio). However, its role in pregonadal differentiation of the sexes has not been resolved. This review examines possibilities for the mechanisms by which Sex reversal Y could exert an influence on those differences, including a role in regulating non‐coding RNAs. The possibility that these mechanisms vary between these two species, long separated by evolution, is also raised.