As a result of a revision of the lichen genus Thelotrema in the Sakhalin Region (Russian Far East), two species are reported as new to the region. Thelotrema diplotrema is recorded for the first time in Russia, and T. suecicum is reported for the first time in Asia. T. diplotrema previously known only from evergreen forests in tropical and subtropical regions of Africa, Australia, and Asia, was found in an old-growth forest with bamboo understory on the bark of deciduous trees on Kunashir Island. This finding represents the northernmost locality of the species in the temperate zone. T. suecicum, a widespread lichen of rainforests and wet montane forests in the cool-temperate zones of the Northern and Southern Hemispheres (Europe, North and South America, Australia, and New Zealand), was collected in a warm, humid riparian forest on the bark of Alnus hirsuta in southern Sakhalin Island and in an oak forest on the bark of Quercus crispula on Iturup Island. Following this revision, three species of Thelotrema are confirmed for the Sakhalin Region, including the previously known T. lepadinum. Detailed morphological, anatomical, and ecological descriptions are provided, along with illustrations, diagnostic features of similar species, and an identification key for the species of Thelotrema and morphologically related taxa occurring in the region. Keywords: broad-leaved forest, cool-temperate zone, corticolous lichens, old-growth forest, tropical and subtropical lichens.