Besides destroying tumor cells directly, radiation also causes an intra-tumoral vasculopathy, which results in vascular occlusion and incompetence. Vascular occlusion causes ischemia, which stimulates the production of angiogenic factors, causing iris neovascularization and neovascular glaucoma. Vascular incompetence causes fluid leakage, interstitial edema, macular edema, retinal lipid exudates, and exudative retinal detachment. The term “Toxic tumor syndrome” was coined by the author to encapsulate all this radiation-induced ocular morbidity. It is important to distinguish toxic tumor syndrome from collateral damage to healthy structures, such as the optic nerve and retina. The first line of treatment is currently anti-angiogenic therapy. If this proves ineffective, intravitreal steroids, transpupillary thermotherapy, or excision of the toxic tumor may be useful. Encouraging results are being reported with prophylactic anti-angiogenic treatment, and this approach is likely to become increasingly successful as more-effective agents are developed and as greater expertise in their use is gained.