We reviewed 22 consecutive patients (26 eyes) with acute retinal necrosis to elucidate whether there was any sign at an early stage to predict poor visual outcome. Final visual acuity of the patients fell into two groups, one worse than 20/600 (15 eyes) and the other better than 20/30 (11 eyes). The patients with poor visual outcome showed diffuse retinal arteritis or arterial obliteration which was associated with reduced amplitude of electroretinographic a and b waves and elevated levels of circulating immune complex, even at an early stage when retinal exudates were still localised to the peripheral fundus. The retinal exudates in these patients extended rapidly to the posterior pole. In contrast, the patients with good visual outcome showed retinal arteritis limited within retinal exudates throughout the course. These signs at an early stage can be used as prognostic factors to manage patients with acute retinal necrosis more constructively.