We have undertaken a clinical and molecular study of 25 females with deletions of the short arm of the X chromosome. We have determined the deletion breakpoints, the parental origin and the activation status of the deleted X chromosomes. Genotype-phenotype correlations suggest that the presence of a single copy of the DFFRX gene, previously postulated as a gene involved in the ovarian failure seen in Turner syndrome, may be compatible with normal ovarian function, and that there may be a gene for Turner-like features located in distal Xp22.3.