Two cases of acute retinal necrosis are reported, the etiology of this affection being priorly defined. The lesions were bilateral in the first case, and retinal detachment developed: the first eye was inoperable, and surgery was unsuccessful for the second eye in spite of a salvage vitrectomy after a classical operation. We therefore treated the second case with immediate and massive corticotherapy, and, mainly, preventive total vitrectomy as soon as the first signs of vitreous retraction appeared and before the occurrence of retinal detachment. This preventive vitrectomy, not previously described to our knowledge, seems to provide favorable results.