The postoperative, six-month visual acuities of 1056 diabetic vitrectomy cases were compared to the following preoperative findings: duration of decreased vision associated with detachments, pupillary responses, iris rubeosis, intraocular tensions, extent of neovascularization, macular status, the ability to recognize entoptic phenomena, bright-flash ERG, and ultrasonography. By comparing these findings to the postoperative visual results, several factors were detected that could be helpful in determining the preoperative prognosis for improved vision. However, major operative complications reduced the incidence of successful visual results from 53% to 22%.