Goals: To evaluate the clearing ability of vitrectomy surgery and some related factors. Subjects: 58 patients (74 eyes) with severe PVR were treated in Fundus Department, VNIO. Methods: descriptive study with postoperative follow up for the success or failure of vitreous clearing. Results: anatomical success in 83,3 percent at discharge. Failure rate was 16,2 percent. Success rate after 2 months was 86,5 percent. Anatomical success rate decreased gradually with time: after 6 months was 75,9 percent and after 12 months was 72,2 percent. The clinical form where there was almost only vitreous hemorrhage (accounted for 31,1 percent): good anatomical outcome was 100 percent. Whereas the clinical form with severe fibro-vascular proliferation (accounted for 39,2 percent): good anatomical outcome was 89,7 percent. If macula off retinal detachment (23 percent), good anatomical outcome was 64,7 percent.If rhematogenous retinal detachment (6,8 percent): good anatomical outcome was 80 percent. Conclusion: vitrectomy in severe diabetic PVR eyes was complicated and subjected to many affecting factors especially clinical forms.