The aim of this paper is to introduce the reader to the history of the Social Insurance Institution [Zakład Ubezpieczeń Społecznych, ZUS] during World War II. Archival materials found in the Historical Committee of the Social Insurance Institution’s Provisional Council [Komisja Historyczna Tymczasowej Rady Zakładu Ubezpieczeń Społecznych], constituting one of the divisions of the Polish Central Archives of Modern Records [Archiwum Akt Nowych], proved to be a most valuable source of information. The available archival documents show that after the German army had invaded the territory of Poland, ZUS units from the areas incorporated into the Reich were in a particularly difficult situation. All their movable and immovable property was confiscated on behalf of German insurance institutions. ZUS units from the area of the General Government [Generalne Gubernatorstwo] were in a better situation – the Germans allowed them to continue their activities, of course, on the condition of full compliance with the occupier’s regulations. Unfortunately, the credit and financial regulations introduced by the German administration within the territory of the General Government resulted in the freezing of the capital assets of social insurance institutions for the whole period of the occupation, which completely deprived them of the right to draw any income from their property.