A collaborative work was carried out by the Spanish and Portuguese International Society for Forensic Genetics Working Group in order to extend the existing data on Y-short tandem repeat (STR) mutations at the 17 Y chromosome STR loci included in the AmpFlSTR YFiler kit (Applied Biosystems): DYS19, DYS385, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393, DYS437, DYS438, DYS439, DYS448, DYS456, DYS458, DYS635, and GATA H4.1. In a sample of 701 father/son pairs, 26 mutations were observed among 11,917 allele transfers across the 17 loci. After summing previously reported mutation data with our sample, mutation rates varied between 4.25 x 10(-4) (95% CI 0.05 x 10(-3)-1.53 x 10(-3)) at DYS438 and 6.36 x 10(-3) (95% CI 2.75 x 10(-3)-12.49 x 10(-3)) at DYS458. All mutations were single step, and mutations in the same father/son pair were found twice.