A retrospective review of cases on file at the Ophthalmic Oncology Center of New York Hospital-Cornell Medical Center, New York, was undertaken to examine the effectiveness of a second course of radiotherapy on retinoblastoma. One hundred four patients were found to have been treated with at least two courses of external beam irradiation to one eye. All but one of the cases were bilateral, the other eye with more advanced disease having been previously enucleated. At the time the decision was made to repeat radiotherapy, 15 eyes could be classified group I, II, or III. Twelve (80%) of these eyes survived. Of the 89 eyes that showed more advanced growth (group IV or V), only two (2.2%) survived. In all, 14 of the 104 eyes wer saved--nine with useful (macula) vision, five without. Second nonocular tumors developed in 18 patients (22.8% of those who survived retinoblastoma itself). There appears to be no increased risk of second tumors from the second course of irradiation.