The various in vivo studies on posterior ciliary arteries and choroidal vasculature reported piecemeal by the author over the past few years have now been collated. A coherent picture of the vasculature emerges which is of considerable clinical significance. The observations show that the posterior ciliary arteries and their branches right down to the terminal choroidal arterioles, the choriocapillaris, and the vortex veins have a segmental distribution in the choroid, and that the posterior ciliary arteries and choroidal arteries function as end-arteries. No special mascular artery supplying the submacular choroid has been found. The posterior ciliary arteries have only supply the choroid but are also the main source of blood supply to the anterior part of the optic nerve, and have an important role in the blood supply of the retina. The clinical significance of this segmental distribution of the uveal vasculature is discussed.