We have produced experimental commotio retinae in 12 owl monkeys by blunt trauma. The ophthalmoscopic and fluorescein angiographic appearance of this contrecoup lesion is identical to the acute traumatic retinal opacity in humans. We examined these eyes by light and electron microscopy from 4 hours to 12 weeks after injury. Immediately after injury, the only abnormality is disruption of the receptor outer segments. From one to six days after trauma, many receptor cells undergo degeneration. The retinal pigment epithelium phagocytoses the degenerating outer segments, occasionally migrating into the retina. There is no extracellular retinal edema. The opacity of commotio retinae seems to represent disrupted receptor cells. Visual loss may result from permanent loss of receptors. The pigment epithelial response to traumatic receptor damage is similar to that observed in experimental retinal detachment and light-induced retinal damage.