The article outlines the achievements of Polish professors who specialized in the treatment of internal diseases. The analysis concerns the scientists who held professorial chairs between 1918 and 1939. The findings were presented in the context of university medical departments. In Poland, in the interwar period, a total of 13 professors held chairs of internal medicine: Zdzisław Gorecki, Władysław Antoni Gluziński, Aleksander Januszkiewicz, Walery Jaworski, Wincenty Jezierski, Jerzy Latkowski, Jan Henryk Lubieniecki, Witold Orłowski, Zenon Orłowski, Roman Rencki, Kazimierz Rzętkowski, Tadeusz Tempka, and Edward Żebrowski. Some of them had been awarded their chairs before 1918. Most of them were successful researchers. Professors Antoni Gluziński and Witold Orłowski were particularly recognized in the scientific world. Gluziński held chairs at Jagiellonian University and then at the University of Warsaw. Orłowski worked at Jan Kazimierz University in Lviv and then moved to the University of Warsaw. In the interwar period, Polish departments of medicine were one of the largest when compared with other departments. Consequently, internal medicine units (assigned to such chairs) were the largest within the departments of medicine in terms of the staff employed. For this reason, most universities decided to divide such units into 2 independent ones. In the years 1918-1939, the field of internal medicine had flourished in Warsaw, Kraków, Poznań, Lviv, and Vilnius; however, the outbreak of World War II would change this forever. After 1945, Lviv and Vilnius were no longer within the territory of Poland, and Polish professors based in those cities moved to join professorial staff at Polish universities.