BACKGROUND Idiopathic hypertrophic pachymeningitis (IHP) is a rare fibrosing inflammatory process of unknown pathogenesis that causes diffuse thickening of the duramater. In spite of the fact that this pathological entity has been linked to specific etiological agents such as syphilis, tuberculosis, mycosis and sarcoidosis, In recent years there has been an increase in the number of patients with IHP of undetermined cause. METHODS 58 year-old female with a long date history of oppressive headaches, frontally located at first, and later generalized, accompanied by weakness and asthenia; urinary incontinence, dizziness, vomiting, and gait ataxia. Physical examination revealed bilateral cerebellar signs, and optic atrophy. Magnetic resonance displayed a diffuse thickening of the falx cerebrii, and cerebellar tentorium, hypointense in T1 and T2- weighted images, and markedly enhanced following administration of intravenous Gd-DTPA. A biopsy obtained from the falx revealed conspicuous fibrosis, and focal chronic inflammatory mononuclear infiltrate. Complementary exams carried out in order to reveal a specific etiologic agent were negative. CONCLUSIONS Due to the variable clinical presentation, and the difficulty to establish the etiology of the pathological process, to make the diagnosis of IHP usually represents a true dilemma. This diagnosis is often made by exclusion.