Five consecutive patients with proliferative diabetic retinopathy who were treated successfully with panretinal photocoagulation subsequently developed a central retinal artery obstruction. Iris neovascularization developed in the affected eye within one to three months after the obstruction in four of the five patients despite the previous laser treatment. Additional retinal ischemia, as occurs in central retinal artery obstruction, appears to promote marked iris neovascularization in a large percentage of patients, even when successful photocoagulation for proliferative retinopathy has been previously administered.