The pathological changes in the choroid and the retinal pigment epithelium in spontaneously hypertensive rats (SHR) aged 42-117 weeks were observed by transmission electron microscopy. Wistar Kyoto rats (WKY) were also studied as normotensive controls. Some of the endothelial cells of the choroidal arterioles and capillaries were degenerated. Focal cytoplasmic necrosis of the arteriolar smooth muscle cells was seen. The choroid showed severe sclerotic changes, and the retinal pigment epithelium was degeneated with dilated basal infoldings and intracellular vacuoles. Long-term hypertension causes degeneration of the outer retinal layer due to the obstructive changes in the choroidal vasculature.