To investigate aqueous humour and vitreous fluid levels of vascular endothelial growth factor (VEGF) and interleukin-6 (IL-6) in patients with central retinal vein occlusion (CRVO) and serous retinal detachment. In twenty patients (20 eyes) with CRVO and 8 patients (8 eyes) with non-ischaemic ocular disease as controls, optical coherence tomography showed that 10 CRVO patients had serous retinal detachment (subretinal fluid with low reflectivity) and 10 patients had cystoid macular oedema (hyporeflective intraretinal cavities). Retinal ischaemia was evaluated from the area of capillary nonperfusion on fluorescein angiograms. To measure VEGF and IL-6 levels, aqueous humour and vitreous fluid samples were obtained during combined pars plana vitrectomy and cataract surgery. Ischaemia was significantly more frequent among the CRVO patients with serous retinal detachment than those with cystoid macular oedema (10/10 vs. 3/10, P = 0.001). Aqueous humour levels of VEGF and IL-6 were significantly higher in the serous patients than the cystoid patients (P = 0.004 and P < 0.001, respectively). Vitreous fluid levels of VEGF and IL-6 were also significantly higher in the serous patients than the cystoid patients (P = 0.007 and P < 0.001, respectively). These results suggest that a marked increase of vascular permeability due to upregulation of VEGF and IL-6 may contribute to serous retinal detachment in patients with CRVO.