Introduction: Hyperostosis frontalis interna is progressive, irregular thickeness of the frontal bone s internal table. It has been associated with a wide range of syndromes, though we know now that it can occur as an independent entity. Etiology is still unclear, but the most probable hyphothesis is alteration of steroid sex hormons, proven in high frequency among postmenopausal women. It is mostly asympthomatic or it has been accidentally diagnosed after endocranial trauma or postmortal. Because of its progression, in some cases it can cause cerebral cortical compression and varible neurological symptoms. Case report: We present a case of 27 years-old women, hospitalized in Neurosurgical Clinic, because of severe headaches lasting for 3 month. The head CT scan showed a massive, expansive lesion in right frontal bone, with spearing of the superior sagittal sinus and skull midline. Bone bulging does not affect outer table of the frontal bone, but only diploic space and inner table. Pathological analysis of the frontal bone showed marked trabecular thickening both cortical and spongy bone, with corticalisation of spongy bone. Haversian canals showed reduction in number and size, and light fibrosis. The lamellas of the spongy bones were enlarged, with prominent interlamellar bridges and the reduction of interlamellar spaces.In purpose of closer determination of etiopathogenesis,we did immunohystochemical analysis of Estrogen, Progesteron and Androgen receptors in dural tissue. Immunohistohemical stain confirmed nuclear expression of Estrogen and Androgen receptors in dural fibroblasts.Progesterone receptors were negative on immune stain. Conclusion: These results could support the hormonal theory of the cause of hyperostosis frontalis interna.

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