This study was undertaken to determine the fluorescein angiographic characteristics of retinoblastomas, to determine the effect of various methods of treatment of these fluorescein patterns, and to determine whether fluorescein angiography can be of value in determining the response to treatment. We performed fluorescein angiography one or more times on 31 patients with retinoblastoma. Small tumors confined to the retina characteristically showed a well-defined pattern of retinal capillaries that filled during the arterial phase and became diffusely hyperfluorescent in the later phases. The fluorescein pattern varied with endophytic or exophytic tumors, depending upon the size of the tumor and the extent of vitreous or subretinal seeding. Following successful photocoagulation of a retinoblastoma, the tumor vascularity is markedly decreased and the tumor is replaced by fibrovascular tissue. Following successful radiotherapy, the tumor vasculature is altered but not typically obliterated. Three cases of presumed spontaneously regressed or arrested retinoblastomas showed much less vascularity than the active viable tumors. It is concluded that fluorescein angiography can be useful in the diagnosis and management of children with retinoblastoma.