The next enlargement was the incorporation of two buildings (nearby but not adjacent) into the institutional structure of the museum: the Casón del Buen Retiro, which is equipped to display up to 400 paintings and which housed the bulk of the 20th-century art from 1971 to 1997, and the Salón de Reinos (Throne building), formerly the Army Museum.
Glavna stavba je bila razširjena s kratkimi paviljoni v zadnjem delu med letoma 1900 in 1960.