The records of 596 consecutive vitrectomy cases performed for complications of diabetic retinopathy were reviewed to determine the incidence of intraoperative and postoperative vitreous hemorrhage and to determine if blood cleared more rapidly in aphakic compared to phakic eyes. Uncontrollable intraocular bleeding occurred in two eyes (0.5%). Vitreous hemorrhage was present on the first postoperative day in 278 eyes (63%). This early hemorrhage cleared in an average of 9.1 weeks in phakic eyes and 3.4 weeks in aphakic eyes. Further vitreous hemorrhage occurred in 88 eyes (23%). Sixty-four percent of later hemorrhages occurred in 88 eyes (23%). Sixty-four percent of later hemorrhages occurred within six months of the operation and 80% occurred within one year. Later vitreous hemorrhage cleared in an average of 16.2 weeks in phakic eyes and 5.3 weeks in aphakic eyes. Of the 311 eyes with vitreous hemorrhage at some time during the postoperative course, twenty-nine eyes (9%) underwent reoperation to remove nonclearing blood. Nonclearing vitreous hemorrhage was the main cause of final visual loss in only 15 (3.4%) of 438 eyes with adequate follow-up, and 6 of these 15 eyes had final vision of 5/200 or better.