BACKGROUND--In patients with diabetic macular oedema and central cysts ischaemia of the retina appears to be an important contributing factor in the pathogenesis of cysts. This study was performed to further elucidate the role of the inner retinal microcirculation in diabetic cystoid macular oedema (CMO). METHODS--Video fluorescein angiography allows visualisation of the macular microvasculature and measurements of the capillary blood velocity (CBV), foveal avascular zone (FAZ), and perifoveal intercapillary area (PIA, characterising capillary density). RESULTS--Twenty three diabetic subjects with CMO, matched diabetic patients without macular oedema (n = 23), and healthy subjects (n = 23) were included. CBV, PIA, and FAZ did not differ significantly among diabetic groups regardless of presence of cystoid changes. CBV was significantly reduced (p < 0.0001) and PIA was more than doubled in both diabetic groups (p < 0.0001) when compared with healthy subjects. Furthermore, FAZ showed a nearly doubled size in diabetic patients without macular oedema (p < 0.01) and a less pronounced enlargement (by 29%) in diabetics with CMO (p < 0.05). CONCLUSION--The results indicate that the retinal microcirculation in diabetic patients is markedly altered when compared with healthy subjects, regardless of CMO presence. In CMO patients the microcirculatory changes are similar to those of diabetic patients without macular oedema. Thus inner retinal perfusion does not contribute to tissue ischaemia leading to cystoid formations in diabetic maculopathy.