To investigate whether interleukin (IL)-6 or vascular endothelial growth factor (VEGF) influences macular edema in patients with central retinal vein occlusion (CRVO). Retrospective case-control study. Twenty-seven patients who had macular edema with CRVO and 16 patients with nonischemic ocular diseases (control group). Retinal ischemia was evaluated by measuring the area of capillary nonperfusion using fluorescein angiography and the public domain Scion Image program, and macular edema was examined by optical coherence tomography. Vitreous fluid samples were obtained at pars plana vitrectomy. VEGF and IL-6 levels in vitreous fluid and plasma were determined with enzyme-linked immunosorbent assay kits. Vitreous fluid levels of IL-6 and VEGF. The vitreous fluid levels of VEGF (median: 435 pg/ml) and IL-6 (median: 51.2 pg/ml) were significantly higher in the patients with CRVO than in the control group (median: 62.4 pg/ml and 1.07 pg/ml, respectively; P = 0.0046 and P<0.0001, respectively). The vitreous fluid level of VEGF was significantly correlated with that of IL-6 (P = 0.0029). Vitreous fluid levels of both VEGF and IL-6 were significantly higher in patients with CRVO who had retinal ischemia than in those without ischemia (P<0.0001 and P = 0.0003, respectively). Vitreous fluid levels of VEGF and IL-6 were also significantly correlated with the severity of macular edema (P = 0.0014 and P = 0.0047, respectively). Both IL-6 and VEGF were elevated in the vitreous fluid of patients with ischemic CRVO and macular edema. VEGF may increase vascular permeability in patients with macular edema and CRVO, whereas IL-6 may also contribute by acting together with or via VEGF. The author(s) have no proprietary or commercial interest in any materials discussed in this article.