Aims To evaluate the relationship of axial length (AXL), intraoperatively assessed posterior vitreous detachment (PVD) status, and surgical outcomes of diabetic vitrectomy. Methods Retrospective, consecutive case series. Clinical records were reviewed for 115 eyes (50 males, 65 females) with more than a 6-month follow-up who underwent diabetic vitrectomy from a single surgeon. Thirty-three eyes had vitreous haemorrhage, 37 had tractional retinal detachment (TRD) threatening the macula, 43 had TRD involving the macula, and two had neovascular glaucoma. AXL was measured preoperatively by ultrasonography, and PVD status was classified intraoperatively: broad vitreo-retinal adhesion as no PVD, PVD at the macular area with attachment at the disc as incomplete PVD, and complete PVD. Results Forty-four eyes had no PVD, 23 had incomplete PVD, and 48 had complete PVD. A majority of the no PVD group had macula off TRD (97.7%), whereas vitreous haemorrhage (68.7%) predominated in the complete PVD group. Longer AXLs were noted in the complete PVD group compared with the no PVD and incomplete PVD groups (ANOVA in three groups P ¼ 0.0001). Univariate analysis showed that AXL had an influence on anatomical success (P ¼ 0.02). Multiple logistic regression analysis yielded that PVD status is a significant predictor of the final best corrected visual acuity (BCVA)420/100, and BCVA420/40 (P ¼ 0.01, P ¼ 0.02). Conclusions Intraoperatively assessed PVD status is a prognostic factor for functional outcomes of diabetic vitrectomy. Shorter AXL was associated with lesser PVD. In eyes with a lack of PVD, careful timing and decision of surgery are mandatory.