The underlying cause of 200 cases of spontaneous vitreous hemorrhage was analyzed. In order of decreasing frequency, the major causes were diabetic retinopathy (54%), retinal break without retinal separation (17%), rhegmatogenous retinal separation (10%), posterior vitreous detachment (7.5%), retinal renovascularization following central or branch vein occlusion (3.5%), and hypertension (2%). Congenital retinoschisis, old uveitis with posterior vitreous detachment, SC hemoglobinopathy with retinal neovascularization, and chronic myelocytic leukemia with retinal neovascularization were less common causes. No cause could be determined in 2.5% of the cases.