As there is no generally accepted treatment for non-inflammatory anterior ischemic optic neuropathy, we have started a randomized, controlled clinical trial on isovolemic hemodilution. In this study all patients received a basic treatment of 75 mg of acetylsalicyclic acid daily. Patients were then randomly assigned to either a group without additional therapy or a group with isovolemic hemodilution. Isovolemic hemodilution was carried out over 6 weeks by several blood-letting procedures and replacement of volume by infusion of hydroxyethyl starch solutions (PCV down to 35-32%). So far, 21 patients have fulfilled the inclusion criteria (symptoms less than or equal to 30 days, no medical contraindications, no giant-cell arteritis), and since they matched for age, duration of symptoms, cardiovascular risk factors, they could be observed for at least 3 months. Although only 1 of 10 control patients hat better visual acuity after 3 months; 6 out of 11 hemodiluted patients had better vision after treatment (p = 0.024). These results indicate that isovolemic hemodilution most likely has a beneficial effect on the visual prognosis of patients with anterior ischemic neuropathy.