Intraocular silicone oil tamponade is being used with increasing frequency as an adjunct to conventional vitrectomy techniques in the treatment of proliferative vitreoretinopathy. When used in patients with aphakia, corneal decompensation is a common long-term complication. In this study, we evaluated the clinical and morphologic changes that occurred in the corneas of 14 rabbits and seven cats when the anterior chamber was filled with silicone oil. Within six days, wide-field specular microscopy showed a 40% reduction in endothelial density in the area of the silicone oil bubble in both groups. Progressive stromal thinning occurred in the rabbit cornea, with gradual development of a retrocorneal membrane at the junction of silicone-endothelial cell contact. In contrast, persistent stromal edema, peripheral vascularization, irregular plaques on the endothelium, and eventual epithelial ulceration and corneal thinning occurred in cat eyes.