Seven diabetic patients experienced severe but transient visual loss after panretinal photocoagulation for proliferative diabetic retinopathy. In all patients, visual acuity decreased shortly after treatment to levels ranging from 5/200 to no light perception. In five of the patients, no observable ocular disease or surgical complications could explain the degree of visual loss. The other two patients developed exudative macular detachments, although it was not clear that this change accounted for their severe visual loss. Vision improved in all patients over a period ranging from nine days to nine months. In five patients, visual acuity returned to within two Snellen lines of the pretreatment level.