Already the first Lithuanian writings and old dialects contain a number of words adopted from other languages. Researchers often disagree on the ways of their entering the Lithuanian lexicon. Some of these loanwords must have come directly from the Germanic languages, mostly German, while others were received from the Slavic languages, mainly Polish, Belarusian or some other language. In this context the problem of the intermediary language is often pertinent. In his book 'Die Germanismen des Litauischen. Teil I: Die deutschen Lehnwörter im Litauischen', K. Alminauskis recorded 2,770 words; of that number about 130 loanwords are of uncertain origin. Sometimes the ultimate form of the borrowing does not help in determining its origin, because the phonetic and morphological structure of the German and Slavic base forms is fully or nearly identical, e.g. Lithuanian 'laterna', German 'Laterne', Latin 'laterna'; Lithuanian 'gruntas', Middle Low German 'Grunt', Polish 'grunt'. These Germanisms are not old borrowings in the Slavic languages, they passed into Polish in the fifteenth and sixteenth centuries. Thus the Lithuanians and the Poles could have adopted them approximately at the same time. Some of them, lacking Polish phonetic and morphological features, could enter the Lithuanian language directly from the Germanic languages. Their sources could be various: the language and dialects of former East Prussia, Low German of Livonia, Baltic German (Baltendeutsch) language, Low German of Hansa merchants, and lastly the German language used in the Grand Duchy of Lithuania. Some words could enter Lithuanian via writings, in the translations of religious texts. It is also probable that some of them were taken over into Lithuanian directly from Latin through the works translated from Latin. They were not used in the spoken language, nor were they found in dialects. As Lithuanian written records are of comparatively late origin, the article presents some information on the history and ethnicities of Prussia. They must give a better understanding of German dialects as a source of numerous German borrowings in Lithuanian. .