BACKGROUND Nonarteritic anterior ischemic optic neuropathy (AION) is the most common cause of visual loss in older patients with optic disc swelling. METHODS In our study all patients with acute AION examined clinically and by fluorescein angiography between 1986 and 1994 were retrospectively reviewed. The prevalence of associated systemic diseases and the results of Doppler sonographic examinations of extracranial vessels were investigated. RESULTS The records of 86 patients (60 male, 26 female) with AION were available. The mean age at the time of onset of AION was 61 years (range 41 to 85 years, SD = 11.9 years). In 50 patients the right and in 36 the left eye was involved. In 36% of the patients optic atrophy of the other eye because of AION was found. The median visual acuity was 0.25 (range, light perception to 1.25). Fluorescein angiography showed diffuse edema of the optic disc in 23% (20/86) of patients and localized segmental edema in 77% (66/86). Statistical analysis revealed a predominant involvement of the temporal quadrants. Ninety-three percent of patients with AION showed underlying systemic diseases. In 15% of these patients the systemic diseases were unknown at the time of onset of the AION; 58% (50/86) of the patients had hypertension, 28% (24/86) had diabetes mellitus, and 37% (32/86) had disorders of lipid metabolism. Seven percent (6/86) of patients showed no risk factors. Doppler sonographic examinations of extracranial vessels revealed hemodynamic relevant stenosis in 11% (6/56), and non stenotic plaques in 28% of patients (16/56). CONCLUSIONS Because of the high percentage of associated systemic diseases in patients with AION a general examination and adequate treatment are necessary.