Orbital growth of the patients treated with enucleation and radiation in infancy for retinoblastoma was studied by roentgenographic measurements. The patients radiated following enucleation without implantation were found to be many in the present series, and the effects of radiation and the insertion of an implant to the development of the orbit in infancy were discussed. Judging from the results of statistical analysis of roentgenographic measurements of the orbit, growth retardation of the orbit radiated after enucleation was greater than that of the orbit only enucleated. Radiation therapy after enucleation for intraocular malignant tumor in infancy should be avoided as much as possible unless the extrascleral invasion is found at operation.