Mutations in hepatocyte nuclear factor-1beta (HNF-1beta) gene cause a subtype of maturity-onset diabetes of the young (MODY5), whose clinical features are pancreatic beta-cell dysfunction, renal malformations, and in some females, internal genital malformations. Recently, we reported the first case of MODY5 and horseshoe kidney. The patient was the only male in a three-generation family with five affected females carrying renal cysts or dysplastic kidney. Diabetes mellitus, horseshoe kidney, and X chromosome monosomy or mosaicism can be observed in Turner syndrome (TS). In particular, diabetes mellitus affects about 50% and horseshoe kidney occurs in approximately 16% of patients. To investigate whether mutations/polymorphisms of HNF-1beta and X monosomy influence horseshoe kidney development, we evaluated HNF-1beta gene sequence in 13 patients with TS and several kidney abnormalities. Analysis of the nine exons including intron-exon boundaries of HNF-1beta revealed the presence in two subjects (15%) of a known intronic polymorphism, IV8+48insC. No specific variants were found. We conclude there is no direct relationship between horseshoe kidney in TS and mutation or polymorphism of HNF-1beta gene, but we speculate that target gene(s) of HNF-1beta, likely mapped on the X chromosome, is/are responsible of the horseshoe kidney formation in TS.