A beneficial visual outcome was achieved in 16 (38%) of 42 eyes into which silicone oil was injected after difficulties were encountered during closed microsurgery for severe diabetic retinal detachment. Without recourse to oil injection, most if not all of the eyes would have remained blind and many would have deteriorated into rubeotic glaucoma or phthisis. The main cause of failed surgery was rhegmatogenous retinal detachment associated with residual or reparative epiretinal fibrosis, and silicone oil appeared to be of value in preventing rubeosis iridis in such cases. Cataract was a significant problem in the successfully treated eyes.