Recent trends in the treatment of retinoblastoma have favored radiation therapy as opposed to enucleation. A major determining factor in selecting radiation therapy is the possibility of useful posttreatment visual function. While the treatment of nonmacular tumors seems reasonable, little information is available about the posttreatment visual outcome of large posterior pole tumors. We treated 17 patients (20 eyes) with group III-V retinoblastoma and large posterior pole tumors with external beam radiation. Visual acuity after treatment ranged from 5/200 to 20/50. Potential posttreatment visual function was difficult to predict using such pretreatment factors as age at diagnosis, funduscopic appearance, and the number, size, and location of the tumors. Surprising visual function was obtained in some patients with multiple large macular tumors. Follow up ranged from 1 to 8 years. No patient developed metastatic disease; however, four patients required subsequent cataract extraction. This study supports the consideration of radiation therapy as the primary treatment in eyes previously felt to have a poor visual outcome.