Beetles and flat bugs living on the decaying wood of aspen (mainly under bark) were collected during expeditions to Finnish and Russian Karelia. Similar searching methods were used, and a comparable number of sites and trees (about 120) were examined on both sides of the border. The fauna on aspen in Russian Karelia was considerably rich. A total of 21 and 5 rare species were found in Russian Karelia and Finnish Karelia, respectively. Within about twenty working hours in Russ. Karelia we encountered two species considered extinct in Finland(Hylochares cruentatusandCyllodes ater)and five considered endangered or vulnerable(Acritus minutus, Rhacopus attenuatus, Uleiota planata, Cucujus cinnuberinusandAnidus truncatus).We suggest that the high number of rare species at the sites studied in Russian Karelia is attributable to the different management history of the forests, particularly to the abundance and continuity of large, dead aspens. Disturbance caused by logging and leaving the non‐marketable trees has probably increased the diversity at some sites in Russ. Karelia. Aspens killed by notching which are common in eastern Finland had a poor fauna.