The development and topographical anatomy of the gorilla frontal sinus are described from late foetal life to senescence and details are given of its pneumo-osteolytic role in relation to that of the other paranasal sinuses. The adult sinus is shown to manifest one or other of two distinct morphological patterns and these to be determined by the more dominant maxillary sinus. Examples of frontal sinus perforative osteolysis are instanced and frontal sinus homologies are briefly discussed.