X-linked congenital generalized hypertrichosis (Online Mendelian Inheritance in Man 307150) is an extremely rare condition of hair overgrowth on different body sites. We previously reported linkage in a large Mexican family with X-linked congenital generalized hypertrichosis cosegregating with deafness and with dental and palate anomalies to Xq24-27. Using SNP oligonucleotide microarray analysis and whole-genome sequencing, we identified a 389- kb interchromosomal insertion at an extragenic palindrome site at Xq27.1 that completely cosegregates with the disease. Among the genes surrounding the insertion, we found that Fibroblast Growth Factor 13 (FGF13) mRNA levels were significantly reduced in affected individuals, and immunofluorescence staining revealed a striking decrease in FGF13 localization throughout the outer root sheath of affected hair follicles. Taken together, our findings suggest a role for FGF13 in hair follicle growth and in the hair cycle.