Thirty-seven patients with bilateral retinoblastoma, groups I, II, and III, were treated with simultaneous bilateral radiation. The median age at diagnosis was 4 months. Twenty-two of these patients were examined because of known history of retinoblastoma. Eight of these 22 patients had no evidence of retinoblastoma on at least one examination before the detection of retinoblastoma, and two had bilateral disease present at birth. Of 74 eyes treated, 39 required additional treatment and 11 ultimately were enucleated. Three patients died of metastatic disease. Seven patients subsequently had second nonocular tumors develop that were both in and out of the field of radiation.