PURPOSE: To assess the effect of prophylactic 360 degrees peripheral retinal cryotherapy in fellow eyes of patients with spontaneous giant retinal tears (GRTs) on the incidence of retinal detachment. DESIGN: Retrospective, noncomparative case series. PARTICIPANTS: Forty-eight consecutive patients (31 male, 17 female) with spontaneous GRTs were included. The average age was 41 +/- 2 years. The average refraction of the fellow eye was -4.0 +/- 0.8 diopters (D). INTERVENTION: Patients underwent vitrectomy and silicone oil tamponade in the affected eye and 360 degrees peripheral cryotherapy in the unaffected fellow eye during the same anesthetic. MAIN OUTCOME MEASURE: Attachment of the retina in the fellow eye was determined clinically by indirect ophthalmoscopy. RESULTS: During a mean follow-up of 84 +/- 10 months after cryotherapy, one patient (2%) experienced a retinal tear without retinal detachment, and three patients (6%) experienced a retinal detachment in the fellow eye. These occurred 18 +/- 9 months after prophylactic treatment and were the result of a small retinal break in two cases and a GRT posterior to the treated area in one case. CONCLUSIONS: Prophylaxis of fellow eyes with 360 degrees cryotherapy appears to be associated with a lower incidence of retinal detachment than that reported in natural history studies. A prospective, randomized clinical trial of such prophylaxis is desirable but would require a sample size of at least 645 patients in each arm of the study, as well as long-term follow-up of at least 5 years to show an unequivocal difference in outcome.