The interest towards the Trans-Onega region of Karelia emerged among researchers from the second half of the 19th c. at the folklore, linguistic, and ethnographic levels, although the researchers have not yet considered traditional medicine as a cultural layer of the ethnos. The problematics of the research is determined by insufficiently studied traditional and non-traditional cultures of the Trans-Onega people, including ethnomedicine. In order to fill this gap, the data from a field journal reposited in the Scientific Archive of the Karelian Scientific Center of the Russian Academy of Sciences are drawn upon. When systematizing the information obtained from the field journal, scientific inquiries into traditional medicine of the Russian and Finno-Ugric peoples were utilized. The proposed research is aimed at the analysis and systematization of the materials of the field journal, which contains information about the traditional medicine of the Russians of the Trans-Onega region in the 1930s collected in the villages of Petry, Longasy, Garnitsy, Migury, Konda, Motalovo, Lelikovo, Koselga, Zinovievo, Sennaya Guba, etc. The research was carried out using the contrastive-comparative method. For this analysis, data were used on the rational and irrational healing practices of one of the groups of the Karelian ethnos, the Ludian Karelians, which is justified by their close contacts with the Russians of the Trans-Onega region. Ludian Kalelians traditionally live in a number of villages and small towns of the south-eastern part of the Republic of Karelia in Olonetsky, Pryazhinky, and Kondopozhsky Districts; hence, the settlement territory of the Ludian Karelians spans approximately 200 km in the eastern part of Olonets Isthmus, from north to south, from the Suna River to the Svir River on its northern tributaries, the Uslanka and Vazhinka Rivers. Based on the research on the traditional medicine of the Russian and Finno-Ugric peoples, we managed to systematize the information obtained from the field journal, distinguishing two groups of healing practices: rational and irrational. According to the journal accounts, in the first half of the 20th c. (1931), among the rational treatment methods of the Trans-Onega people one can identify phytotherapy (plant and herb substances); treatment with substances of animal origin, human excreta, mineral substances, food, precious metals, and combustion products; and physiotherapy, which should be considered as one of the most common methods of traditional medicine, along with phytotherapy. The natural environment (flora and fauna), methods of farming, as well as traditional crafts of the Trans-Onega people reflect in the medicine used. To the irrational methods of treatment one should ascribe the incantation tradition and sorcery. As the result of the conducted research, it was possible to identify similar features in the traditional medicine practices of the Ludian Karelians and Russians of the Trans-Onega region, induced by their long-term residence on the same territory and indicating close contacts between representatives of the two ethnic groups.