The authors report the rare existence of a family that includes an older sister with Pfeiffer syndrome and a younger sister with achondroplasia. Gene analysis of these patients showed a T341P mutation in the FGFR2 gene in the patient with Pfeiffer syndrome, and a G380R mutation in the FGFR3 gene in the patient with achondroplasia. Both mutations have been reported previously. Their parents had no mutation in either locus. This result suggests the possibility that there may be predisposing factors for different FGFR mutations.