This prospective, randomized, multicenter, controlled trial was designed to evaluate the efficacy and safety of intravenous ganciclovir for the treatment of peripheral cytomegalovirus (CMV) retinitis in patients with AIDS. Patients were randomly assigned to receive either immediate treatment, intravenous ganciclovir, 5 mg/kg twice daily for 14 days followed by 5 mg/kg once daily for 14 weeks, or deferred treatment. Patients randomized to deferred treatment whose retinitis progressed were offered ganciclovir. Of the 22 patients randomized to deferred treatment who were included in the final analysis, 20 were found to have progressive CMV retinitis compared with 10 of the 13 randomized to immediate treatment. The median time to progression in the deferred treatment group, as determined by a masked fundus photography reading center, was 13.5 days compared with 49.5 days in the immediate treatment group (mean +/- SD, 19.3 +/- 4.1 vs. 66.4 +/- 14.0; P = .001, log rank test). These data indicate that ganciclovir delays the progression of CMV peripheral retinitis in persons with AIDS.