Introduction. Hypertrophic pachymeningitis is a clinical condition that is caused by a diffuse or localised thickening of the dura mater. It predominantly affects males and manifests as chronic headache, with or without association to neurological manifestations, such as paralysis of the cranial nerves, cerebellar ataxia and neuro-ophthalmic complications. Case report. A 61-year-old male, with no relevant past history, who, one month before admission, had begun to suffer from right fronto-temporal headache that irradiated to the ipsilateral orbital region and was more pronounced at night. A week later he was affected by a decrease in visual acuity in the right eye and two weeks later he noted the presence of right palpebral ptosis, while the headaches increased. The examination showed: right palpebral ptosis with global ophthalmoparesis with predominance of adduction and abduction, and diminished photomotor reflex in the right eye. The visual acuity of the right eye was reduced and the palpebral fissure was 0 in the right eye. The fundus oculi was normal. Infectious and non-infectious causations of meningitis were precluded. Magnetic resonance imaging revealed a diffuse thickening of the supratentorial and infratentorial meninges, as well as diffuse uptake of the paramagnetic substance; thickening of the mucus in both paranasal maxillary sinuses was also observed. A meningeal biopsy study confirmed the existence of hypertrophic pachymeningitis. Treatment was established with prednisone and the clinical symptoms improved. Conclusions. Idiopathic hypertrophic pachymeningitis is an underdiagnosed condition that must be taken into consideration in cases of patients with a history of subacute or chronic meningitis in which infectious and non-infectious causations have been precluded, and high-dose steroid treatment must be established. © 2009, Revista de neurologia.