We report a series of 21 consecutive patients seen at the Ophthalmology Department of the University Hospital Zurich, Switzerland, with the arteritic form of anterior ischemic optic neuropathy (AION). 19 patients had giant cell arteritis, one had periarteritis nodosa and one had cP-arteritis. They comprised 11 men and 10 women, ranging in age between 66 and 88 years. The median age was 80. We analyzed the course of events in each case before and after involvement of the first eye, as well as the frequency and possible causes of involvement of the second eye. The diagnosis was regarded as delayed when, despite typical signs, symptoms amd laboratory abnormalities, systemic vasculitis was not considered in the differential diagnosis. Treatment was considered inadequate if, following visual loss in one eye and diagnosis of a systemic vasculitis, a dose of 1 mg/kg prednisone or less was given, and/or the initial dose was reduced by more than 50% during the first month. Of 21 patients, 10 suffered bilateral visual loss. 8 of these 10 patients became legally blind. In 13 out of 21 cases there was no delay in diagnosis and treatment was adequately given. All 11 patients with unilateral involvement, who did not suffer a substantial loss in quality of life, belong to this subgroup. In 8 cases diagnosis was either delayed or treatment was inadequate. All of these patients had bilateral ocular involvement. In one patient, visual loss in the second eye could not be avoided despite correct diagnosis and treatment (M.A., No. 1). In this patient the interval between involvement of the first and second eye was very short (3 days). One patient had a mature cataract in the first affected eye and sought medical help only after his good eye became involved (K. F., No. 15). In this report we would like to draw attention to the extremely poor visual prognosis due to frequent bilateral ocular involvement in giant cell arteritis. Corticosteroid treatment cannot restore vision in the already affected eye, but it is, in the majority of cases, highly effective in preventing visual loss in the second eye. Thus, it is crucial to begin treatment immediately, to start with a high dose (preferably 1 g methyl-prednisolone i.v.), and to continue high-dose oral treatment long enough to prevent delayed visual loss in the second eye. The most vulnerable period appears to be the first month following involvement of the first eye. Caring for patients with giant cell arteritis who have lost vision in one eye is a challenge to all involved physicians. It resembles a "high-wire act" with the threat of blindness on the one hand and the dangers of long term corticosteroid treatment on the other. An interdisciplinary approach with ongoing communication between the family physician and the ophthalmologist is required.