The authors present aspects of the skull base in trigonocephalic children. Different patterns on clinical anthropometric investigation, bidimensional computer tomography (CT) scan and three-dimensional (3D) CT scan were studied. We present a series of 27 cases of trigonocephaly operated on in the department of pediatric neurosurgery at the Hôpital des enfants La Timone in Marseille since 1975. The skull base has been studied with CT scan in 12 patients and in 5 a 3D CT reconstruction was performed. A control series of 27 children without synostosis has been studied with the same patterns. We have analyzed in 3D, the volume of the anterior fossa related to the orbital volume, the permeability of basal sutures and the spatial orientation of petrous, sphenoid and zygomatic bones. An analysis of nasoethmoidal complex was performed in relation with hypotelorism. CT scan allows the study of the opening of orbital, nasion-pterional angles and the clinopterional angles, as well as nasion-clinoidal and bipterional distances. A computerized analysis of these data compared with normal skull base permits a new approach to these malformations and the necessity for subdivision of trigonocephaly.