We report on a series of 135 consecutive cases of pars plana vitrectomy for proliferative diabetic retinopathy (average period of observation was 13 months). BSS was used in 69 eyes and silicone oil was used in 66 eyes as a vitreous substitute, the indications for silicone oil in these cases were the presence of several retinotomies or retinectomies as well as sharply increased risk for rebleeding. Postoperatively and after a minimum follow up of 6 months (55 eyes) the two groups with BSS or silicone oil achieved comparable functional results despite the different anatomical preoperative situation. Thus 18 out of 23 eyes of the silicone oil group, originally with detached macula and visual acuity of HM or FC, achieved a visual outcome of greater than = 0.02, showing the best postoperative result. In the BSS-group, with attached macula prior to the operation and same visual acuity, this result is attained by 27 out of 35 eyes. We interpret these figures as meaning, that silicone oil in proliferative diabetic retinopathy reduces some of the problems connected with more advanced retinal changes like retinal detachment and rebleeding thereby allowing a visual outcome which corresponds to the macular condition.