Purpose: To investigate the factors that influence the visual-changing pattern in proliferative diabetic retinopathy even after successful vitrectomy. Methods: One hundred and forty-seven consecutive eyes were retrospectively reviewed for 6–48 (average 20) months, and were divided into the following 4 groups based on their changing pattern of vision: group A, the visual acuity improved postoperatively and maintained the maximal corrected vision throughout the observation period (n = 49); group B, the visual acuity improved postoperatively but deteriorated thereafter (n = 68); group C, the visual acuity remained the same as before operation (n = 17), and group D, the visual acuity deteriorated immediately after vitrectomy (n = 13). Various issues including systemic conditions, blood tests, preoperative ocular findings, the operative procedures and postoperative complications were reviewed based on the patient records. These issues were analyzed by Spearman’s rank correlation, χ<sup>2</sup> test, an analysis of variance (ANOVA) and the Kruskal-Wallis test. Finally, the discriminate factors between groups A and B were examined by a stepwise logistic regression analysis. Results: The following tendencies were observed in all 4 groups: younger patients tended to show a better visual-changing pattern (p = 0.02); patients with younger age at diabetes onset had a better visual-changing pattern after vitrectomy (p = 0.001), and a lower hemoglobin (Hb) A1c level is associated with a better visual changing pattern (p = 0.017). Preoperative rubeosis and macular detachment were frequently found in groups C and D, as well as postoperative rubeosis, vitreous bleeding and retinal detachment. Finally, a stepwise logistic regression analysis showed both fibrovascular proliferation (p = 0.016) from the optic disc and postoperative macular disease (p = 0.0009) to be significant factors for differentiating group A from group B. Conclusions: In addition to the factors which have already been indicated to affect the visual outcome of a vitrectomy, preoperative findings such as optic disc fibrovascular proliferation and postoperative macular disease were found to affect the visual-changing pattern after a successful vitrectomy. The optimal timing of surgery is very important not only in order to obtain good visual acuity but also to maintain good vision even after a successful vitrectomy.