Though allele frequency data for a variety of X chromosomal short tandem repeat (STR) markers in a range of populations have been reported, fewer studies of mutation rates in these same markers or populations are available. In order to address possible mismatches during kinship analysis due to mutation, a robust estimate of the rate of mutation must be established. Here, mutation rates in three US populations have been determined for a total of 15 markers (DXS6789, DXS9902, DXS7132, DXS7130, DXS6795, DXS10147, DXS8378, DXS7423, HPRTB, DXS101, DXS7424, GATA31E08, GATA172D05, GATA165B12, and DXS6803). Eighteen mutations over 20,625 meioses were observed, and the overall X STR mutation rate in this study was found to be 8.73 × 10(-4) (95 % CI, 5.2-13.8 × 10(-4)). A review of published mutation rate studies revealed similar findings in other global populations, and allowed the compilation of a combined dataset of 81,310 meioses which can be employed by the forensic community.