Using questionnaires completed by 284 national park field workers I evaluated the occurrence and population dynamics of large mammals from 1996 to 2005 in all 23 Polish national parks. A total of 29 species were found: 15 carnivores, 8 even-toed ungulates, 2 lagomorphs and 4 large rodents. The greatest population growth was seen in the beaver Castor fiber, the red fox Vulpes vulpes, and three non-native species (American mink Mustela vison, racccoon Procyon lotor and fallow deer Dama dama) while the greatest population decline occurred in two other non-native species (muskrat Ondatra zibethicus and mouflon Ovis orientalis musimon) and to a lesser degree in the native brown hare Lepus europaeus. The richest and most natural large mammalian fauna occurred in the Carpathian parks (Bieszczady NP, Magura NP, Tatra NP and Pieniny NP) as well as in the eastern part of the country (especially Białowieża NP and Biebrza NP), and the poorest was found in the Sudeten parks and in the west. There was a statistically significant correlation between mammal species richness and park size, longitude as well as the degree of disturbance in and around the park (negative correlation).