Apert syndrome is a clinically distinctive condition characterized by craniosynostosis, mid-face hypoplasia, and severe symmetrical syndactyly of the hands and feet. Recently, mutations of the fibroblast growth factor receptor 2 (FGFR2) gene have been associated with several craniosynostosis conditions including Apert, Crouzon, Jackson-Weiss, and Pfeiffer syndromes. Mutations detected in Crouzon, Jackson-Weiss, and Pfeiffer syndromes are located at several sites in the FGFR2 gene. However, the mutational spectrum in Apert syndrome is remarkably narrow. Mutations detected thus far in Caucasian patients with this syndrome are exclusively transversions from cytosine to guanine at either nucleotide position 934 (C934G) or 937 (C937G) in the FGFR2 gene. To examine the possibility that the narrow mutational spectrum in Apert syndrome was a result of racial or environmental predilection, we studied three Apert syndrome patients from two unrelated Japanese families for C934G and C937G mutations. The C934G mutation was found in all three patients. This is the first demonstration of FGFR2 gene mutations in Japanese patients. Our evidence that the C934G mutation identified in Caucasian patients also occurs among Japanese patients excludes the possibility of racial or environmental predilection for this mutation. Nucleotide position 934 is a mutational hotspot of the FGFR2 gene in Japanese patients as well, although the mechanism by which the mutation occurs remains to be clarified. Whether C937G is a mutational hotspot in Japanese patients as well remains to be determined.