The Allegheny River Islands Wilderness (ARIW) consists of seven islands located along 90 km of the Allegheny National Wild and Scenic River in northwestern Pennsylvania. I surveyed riparian plant communities in the ARIW to provide an inventory of the species composition and distribution of the alien flora and to identify species of potential management concern. Forty alien plant species (17.8% of the total surveyed flora) were tallied from 42 survey sites across the seven islands of the ARIW. The largely herbaceous floodplain scour community supported the greatest number of alien plant species (35 species; 18.9% of the community flora), followed by the Acer saccharinum–Platanus occidentalis floodplain forest community (23 species; 16.8% of the community flora) and the P. occidentalis–Carya cordiformis–Ulmus rubra floodplain forest community (14 species; 12.4% of the community flora). Ten alien plant species (24.4% of the alien flora) occurred across all three community types. The alien flora of the ARIW included a range of species with varied ecological impact potential, distribution across plant communities, and difficulty of control. Potential control strategies for alien plant species in the ARIW must address the influence of an altered hydrologic regimen as well as control protocols for specific species on the islands and surrounding river corridor.