Two hundred eighty consecutive vitrectomies in diabetic patients were studied retrospectively. In 15 eyes, interlacing fibrin-like strands appeared on the surface of the retina and behind the iris plane from two to 14 days postoperatively. One or two days later, a gelatinous mass formed in the center of the vitreous activity, leading to the development of tractional retinal detachment and rubeosis iridis with neovascular glaucoma. Large doses of systemic and topical corticosteroids reversed the fulminating course of this complication in six of 15 eyes. The combination of lens surgery or scleral buckling procedure with vitrectomy, and the presence of retinal detachment preoperatively seemed to predispose to this complication. It is possible that multiple surgical procedures performed during the same operation cause an increase in vascular permeability resulting in the formation of a gelatinous, fibrin-like material in the diabetic eye.