SF1 and disorder of sexual differentiation: Gerard Conway, a colleague at the adult DSD clinic at UCLH, recently said: “If the phenotype doesn't make sense, think of SF-1.” This may not always be true, but steroidogenic factor-1 (SF-1/NR5A1)-related phenotypes have expanded greatly in recent years, and the report of Swartz et al. [1] in this issue of Hormone Research in Paediatrics adds to the emerging picture.