Detailed mapping in the area of Panion Hill (SE Attica, Greece), revealed the existence of three metamorphosed lithological units which are separated by major tectonic contacts. The lower unit is located at the western part of Panion Hill and comprises marble - schist alternations that pass transitionally to massive dolomitic marbles of probable Triassic age. The intermediate unit comprises exclusively massive to thick bedded marbles that occupy the central and eastern part of the hill. The upper unit can be observed mainly at the foothills of Panion and comprises HP/LT schists, exhibiting greenschsist facies retrograde metamorphism. The contact between the lower and the intermediate unit is a low-angle normal fault, dipping to the east-southeast whereas the upper unit, in most cases is juxtaposed against the intermediate and lower units by high angle normal faults. These contacts accommodated the exhumation of the lowermost metamorphic formations of Attica at least in the last stages. The overall structure resembles that of Mt. Hymittos (east of Athens), where the Vari Schists and Dolomitic Marble formations (Vari – Kirou Pira Unit, VKPU) underlie tectonically the Lower Marble, Kesariani Schists and Upper Marble formations (Hymittos Unit, HU). Based on lithological and structural similarities the lower unit of Panion Hill is considered to be part of the Vari – Kirou Pira Unit and the intermediate unit part of the Hymittos Unit, respectively. The upper unit of Panion Hill belongs to the allochthonous Lavrion Unit. The existence of a major tectonic contact separating formations of VKPU and HU in several outcrops in SE Attica signifies that it is of no local character. Furthermore, it supports the suggestion of dividing the relatively autochthonous unit of Attica into two distinct units: the upper Hymittos Unit and the lower Vari – Kirou Pira Unit, the latter standing for the actual autochthonous unit of SE Attica.