The first of the big projects envisioned and implemented by the Onassis Foundation was built on an 8.000m2 plot of private land on Syngrou Av. After it was completed and equipped it was handed over, fully operational, to the Greek State on October 6,1992.

The building was designed by the architects specialists in hospital design - Llenelyn Davies Weeks and constructed by J&P -overseas. It has a total surface area of 21.360m2, consisting of a basement and nine floors above ground, arranged around a central atrium. The architects’s brief was to design a “state of the art” building with a memorial character and a form with “Hellenic influences”. The building has become a landmark for Athens.

In 2004 ,a concept architectural design was prepared , for the extension of the building, of total surface 7.000m2 , attached to the existing and with the same morphology, in order the two buildings to constitute an homogenous complex.