The fundus fluorescein angiograms of 13 patients with visual disturbance due to biopsy-proven giant cell arteritis (11 with anterior ischemic optic neuropathy (AION); 2 with visual obscurations only) were compared with the fluorescein angiograms from 33 patients with acute nonarteritic AION and 23 age-matched normal eyes. In all 13 patients with giant cell arteritis, the fluorescein angiograms showed a significant delay of choroidal filling time (mean 69 seconds) in comparison with either normal subjects (mean 5.8 seconds) or patients with nonarteritic AION (mean 5.5 seconds). In patients presenting with acute AION, the finding of delayed choroidal filling on fluorescein angiography should raise the index of suspicion of giant cell arteritis and lead to prompt investigation and treatment.