The National Parks System of Argentina (NPSA) comprises 33 protected areas (3,546,044 ha) and represents 1.25% of the country's total area. The goal of this work is to provide the first description of the distribution of invasive mammal species within the NPSA based on various information sources in order to assist future decision making concerning management strategies for these species. The occurrence of invasive mammals in different areas of the NPSA was determined from diverse sources: internal reports, mammal collections, survey questionnaires, and literature review. Sixteen invasive species are established within 26 of the 33 (78.7%) protected areas of NPSA. The most widespread species is European hare (Lepus europaeus Linnaeus), followed by wild boar (Sus scrofa Linnaeus). Highest relative invasion indices are recorded in areas within the Patagonian forest, followed by areas in the Patagonian steppe. Two clearly different situations are present in the protected areas of the NPSA: (1) areas situated within the southern ecoregions, where invasive species have mostly been introduced for big game hunting purposes or fur farming, and (2) areas situated within the northern ecoregions, where the dominant invaders are feral species linked to cattle farming activities.