Records from islands in Lake Onego list 145 species of aphyllophoroid fungi, including Gloeophyllum protractum, Junghuhnia collabens, J. pseudozilingiana, Polyporus badius, Rigidoporus crocatus, and Tyromyces fissilis, which are red-listed in the Republic of Karelia (2020). Data are reported on the distribution of 4 species new for the Karelia onegensis province. Specimens of all the new records are kept in the mycological herbaria of the Karelian Research Centre (PTZ). A majority of aphyllophoroid fungi on islands in Lake Onego were found on deciduous trees (94 species), and 53 species were recorded from coniferous trees. The greatest numbers of fungal species were found on rowan (39), aspen (38), pine (32), spruce (25), willow (25), and birch (21). Locations of 18 indicator and specialized species of old-growth forests were found on the islands. The species richness of aphyllophoroid fungi on each island depended on a set of factors – tree species composition and presence of deadwood in different stages of decay, proportion of the forest cover (open rock), different types of habitats, and the degree of anthropogenic disturbance. The island size was not significant. Brief information about agaricoid fungi is also provided.