Sebastian Poszywak, author of “Mój pamiętnik z wojny światowej”, was a soldier who fought in an Austro-Hungarian regiment. Together with his troops he fought on the Italian front during World War I. The diary he kept is full of local names, both Polish and Slovenian, as well as German and Italian. The article presents the onymic awareness of the author of the diary, examines various forms of toponyms that sounded foreign to the soldier from the Podkarpacie region, emphasizing the structures of Slovenian (e.g. Brestovica pri Komnu – Brestowice, Brestawice, Brestowica) and Italian (e.g. Medeazza – Medyjaca, Madyaco) local names. The text also takes account of the history of onomastic research on proper names contained in the diaries. The article is a contribution to further onomastic analyses of other onymic categories of peasant diaristic texts.