PURPOSE To determine whether a decrease a arterial blood pressure may be a risk factor in occurrence of non-arteritic anterior ischemic optic neuropathy (NAION). METHODS Two groups of patients were followed up: group I--with arterial hypertension treated with hypotensive therapy and without NAION.; group II--with arterial hypertension treated with hypotensive drugs and NAION previously diagnosticated--Ophthalmologic evaluation (including visual acuity, visual fields, intraocular pressure, slit lamp and ophthalmoscopic evaluation, relative afferent pupillary defect) was performed. Systemic evaluation consist in blood tests (including erythrocyte sedimentation rate and Creative protein), echocardiography and 24-hours blood pressure monitoring. RESULTS A significant low blood pressure was found at the patients with affected eyes (with NAION) in comparison to the patients with unaffected eyes. CONCLUSIONS Decrease of blood pressure may be considered a characteristic risk factor of NAION, leading to a vascular insufficiency in the optic nerve head.