The authors relate a clinical and radiological (X Ray and TDM tridimensional) study with an anthropological (dry skulls) study of plagiocephaly. The aim is to find with the aid of a physical examination, some anatomic parameters which permit to differentiate cranial asymmetry with coronal premature synostotic suture from functional deformation with extracranial outset. The term plagiocephaly is used to define forehead asymmetry. It is necessary to study orbital rim, nasal root, malar eminence, ear and chin mid point position. The morphology of the skull is important to look: frontal flattering and also occipital flattering or bulging, contra-lateral frontal and pterional aera bulging. The authors conclude that a single parameter is necessary to differentiate the two kinds of plagiocephaly: the petrous bone position on the flattened frontal side: sagittalisation: fonctionnal plagiocephaly; frontalisation: synostotic plagiocephaly.