In 45 eyes of rhesus monkeys, five types of central retinal vascular occlusion were produced by lateral orbitotomy: group 1, central retinal vein occlusion (CRVO) alone; group 2, CRVO with simultaneous central retinal artery (CRA) occlusion; group 3, CRVO with transient clamping of the CRA for either 2 to 2 1/2 hours (group 3A) or 6 to 7 1/2 hours (group 3B); and group 4, CRVO with segmental retinal ischemia. The eyes were examined by fundus photography and fluorescein angiography for up to nine months. Group 1 developed venous stasis retinopathy (VSR) and group 3B hemorrhagic retinopathy (HR). In group 4 the ischemic and nonischemic segments of the retina developed segmental HR and VSR, respectively. Groups 2 and 3A developed neither VSR nor HR. Retinal capillary obliteration occurred in groups 2 and 3B and in the ischemic part of group 4, starting one to three weeks after the occlusion and progressing thereafter. These studies indicate that clinically co-called CRVO consists of two distinct entities: VSR and HR, with retinal ischemia playing an important role in the production of HR. On the basis of the present and other available information, the pathogenesis of CRVO was concluded to be multifactorial.