Radiotherapy result was analyzed in 23 children with retinoblastoma treated in Seoul National University Hospital from 1980 to 1987. Three (17%) had bilateral tumor at diagnosis. Among 20 children with unilateral retinoblastoma 13 children got radiotherapy after enucleation, 2 were treated with radiotherapy alone, and 5 were delivered with radiotherapy after relapse. Of 15 non-recurrent unilateral tumors, there were 5 stage II children, 8 stage III, and 2 stage IV by staging system proposed by St. Jude Children's Research Hospital. Chemotherapy was combined when resection margin of the optic nerve was positive or when malignant cell was found in SCF. Of 12 children who completed radiotherapy, local or distant failure was not found but 2 cases of relapse at the contralateral retina were observed. Their 5 year survival rate was 82.2%. Another case of contralateral relapse was detected in children who was treated with radiotherapy alone. Thus overall frequency of the bilateral disease was 33%. Prognosis of recurrent tumors were so poor that no cases of CR was obtained and that 3 year survival rate was 20%. Two of 3 bilateral cases at diagnosis were in NED status. Complication were sunken orbit only. Result of radiotherapy was so good in early stage or small bulk tumor that treatment delay after diagnosis must not be allowed.