OBJECTIVE Although the association of cystoid macular edema with peripheral choroidal melanoma has been studied previously, the pathogenesis of cystoid macular edema as evaluated by light and electron microscopy remains controversial. We evaluated the cause of cystoid macular edema at the retinal capillary level. METHODS We clinicopathologically correlated petaloidlike changes noted on fluorescein angiography with the corresponding morphologic changes, as documented by retinal trypsin digest preparation. RESULTS The angiographic foci of fluorescein leakage were found to correspond to sites of endothelial cell proliferation that resembled intraretinal microvascular abnormalities in the retinal trypsin digest preparation. CONCLUSIONS The source of cystoid macular edema at the level of the retinal capillary network are intraretinal microvascular abnormalities resembling endothelial cell proliferation. We examine the relationship between endothelial cell proliferation and vascular leakage.