PURPOSE:To study the relationship between intraretinal optical coherence tomography (OCT) and fluorescein angiography (FA) findings in eyes with diabetic macular oedema (DMO). METHODS:We carried out a retrospective observational case series. Thirty eyes with previously untreated DMO underwent FA and OCT. The same ETDRS template was overlaid on the FA images in order to compare OCT and FA. Transfoveal linear high-resolution OCT scans (at the 0- and 90-degree meridians) and FA pictures were compared according to the ETDRS rings. RESULTS:Six distinct patterns of intraretinal changes in OCT correlated with changes in FA: (a) focal angiographic leakage did not correspond to any obvious intraretinal abnormality in OCT in four eyes; (b) localized thickening of the outer nuclear layer in OCT corresponded to focal leaking microaneurysm (focal oedema) in FA in 11 eyes; (c) diffuse thickening of the outer nuclear layer in OCT corresponded to diffuse angiographic leakage in 21 eyes; (d) cystoid expansion of the outer nuclear layer was found in seven eyes with a petaloid angiographic pattern of leakage; (e) cystoid expansion of the inner nuclear layer was found in relation to honeycomb angiographic oedema in five eyes, and (f) serous detachment of the fovea in OCT did not correspond to any distinct finding in FA in four eyes. CONCLUSIONS:Intraretinal abnormalities found in OCT correlate systemically with changes in FA. Very early DMO morphological changes may be seen better with FA than with OCT. Serous detachment of the fovea is seen in OCT, but not in FA. The combination of OCT and FA is useful in facilitating understanding of the pathophysiological changes that occur in DMO.