Between February 1974 and August 1987, we treated 67 retinoblastomas in 47 eyes of 45 patients with cryotherapy (triple freeze-thaw technique). Overall, cryotherapy eradicated 53 (79%) of the tumors, whereas additional treatment with episcleral plaque radiotherapy, external beam radiotherapy, or enucleation was necessary in 14 (21%) of the tumors. Tumor destruction was achieved with one or more cryotherapy treatments in all cases in which the tumor was no greater than 2.5 mm in diameter and 1.0 mm in thickness, and in which the tumor was confined to the sensory retina without seeding into the adjacent vitreous humor. We therefore recommend cryotherapy in such cases. Cryotherapy alone failed in 14 larger tumors, ten of which had clinical evidence of vitreous seeding by tumor cells. Cryotherapy is therefore contraindicated in cases of vitreous seeding or if the tumor exceeds 3.5 mm in diameter and 2.0 mm in thickness. Cryotherapy can be successful for tumors up to 3.5 mm in diameter and 2.0 mm in thickness, but more than one treatment may be necessary.