Five patients with isolated retinoblastoma lesions were successfully treated by cryotherapy. The lesions ranged in size from one half to 7 disc diameters and in elevation from +2 to +10 diopters. The special features of a modified technique for freezing large tumors include the use of a cryoapparatus with a limited cooling capacity, firm indentation of the sclera under the tumor with the tip of the cryoprobe, a repeated, freeze-incomplete-thaw-and-freeze cycle until an iceball is formed and maintenance of the iceball on the tumor for one minute before complete thawing, freezing the retinal vessels and retina around the tumor, and repetition of cryoapplications for lesions which persist after initial treatment. Follow-up of the patients for two to four years revealed no recurrence of the lesions.