Summary The shape of the anterior part of the anterior cranial fossa undergoes important changes in the postnatal life depending on the degree of pneumatisation of the ethmoid labyrinth and/or the frontal sinus. There exist three possibilities in these relations: 1) From the newborn period up to 9 years of age, in the majority of the cases the cribrous plate is situated at the level of the roof of the ethmoid labyrinth with the width of the ethmoid incisure corresponding to the width of the cribrous plate. 2) In the period from 9–35 years of age, in the majority of cases, the ethmoidal cells are partly or completely incorporated into the floor of the anterior cranial fossa with the width of the ethmoid incisure corresponding to the number of cells forming the floor of the anterior cranial fossa. 3) In the period from 35–80 years of age, the cribrous lamina is in the majority of cases lowered due to the intensive development of the frontal sinus. The medial wall of the ethmoid labyrinth consists of a thin bony strip, the width of which depends upon the degree of lowering of the cribrous plate. Adequate CT imaging may clarify the situation.