The causes of 653 cases of spontaneous vitreous hemorrhage were evaluated. The four most common causes, accounting for over 84% of the cases, were diabetic retinopathy (34.1%), retinal break without retinal detachment (22.4%), rhegmatogenous retinal detachment (14.9%), and retinal vein occlusion (13.0%). Other diagnoses accounting for a significant number of cases of spontaneous vitreous hemorrhage included posterior vitreous detachment, retinal vasculitis, senescent macular degeneration, intraocular tumor, and retinopathy of prematurity. The remaining, uncommon, diagnoses accounted for less than 5% of the cases.