The PowerPlex® Y 23 System (Promega) is a short tandem repeat (STR) multiplex that allows co-amplification of 23 gonosomal Y-STRs, combining 17 loci commonly included in commercially available kits (DYS389I, DYS448, DYS389II, DYS19, DYS391, DYS438, DYS437, DYS635, DYS390, DYS439, DYS392, DYS393, DYS458, DYS385a/b, DYS456, and Y-GATA-H4) and six new loci (DYS481, DYS549, DYS533, DYS643, DYS576, and DYS570) with the last two being rapidly mutating Y-STRs (RM Y-STRs). In order to assess the possible gain in forensic efficiency provided by the six additional markers, a population sample of 410 unrelated healthy males originating from Northeast Italy (Veneto, Trentino Alto Adige, Lombardia, and Friuli Venezia Giulia regions) was typed. The data (335 of the 410 samples) are available in the Y chromosome haplotype reference database under accession number YA003327. Overall, 410 unique haplotypes were found corresponding to a global haplotype diversity (HD) of 0.999994 with a discriminatory capacity (DC) of 100%. Allelic microvariants, null alleles, and duplications were detected. Pairwise genetic distances (R(ST)) calculated among neighboring European reference populations revealed no significant differences. Furthermore, for studying Y-STR mutation rates, 90 father-son pairs, in which the fathers were already included in the full dataset, were tested. On a total of 2,070 meioses considered, eight single-step mutational events were observed, two of which within the same father-son pair and the average mutation rate was 3.38 × 10(-3) per locus per generation (95% confidence interval, 1.36 × 10(-3)-6.95 × 10(-3)).