Currently, two of the most widely used X-chromosome STR (X-STR) multiplexes are composed by ten (GHEP-ISFG decaplex) and 12 markers (Investigator Argus X-12 Kit). The number of markers included is a drawback for complex relative testing cases, likewise the large size of some amplicons difficult their application to degraded samples. Here, we present a new multiplex of 17 X-STRs with the aim of increasing both the resolution power and forensic applicability. This newly proposed set includes the X-STRs of the GHEP-ISFG decaplex, four X-STRs from the Investigator Argus X-12 Kit, three of them also included in the decaplex, and six additional more. In order to ensure the allele designation, an allelic ladder was developed. The validation of the present multiplex was carried out according to the revised guidelines by the SWGDAM (Scientific Working Group on DNA Analysis Methods). A total of 488 unrelated individuals from four different continents were analyzed. The forensic efficiency evaluation showed high values of combined power of discrimination in males (≥0.999999996) and females (≥0.999999999999995) as well as combined paternity exclusion probabilities in trios (≥0.99999998) and duos (≥0.999996). The results presented herein have demonstrated that the new 17 X-STR set constitutes a high-resolution alternative to the current X-STR multiplexes.