Cytomegalovirus retinitis is the most frequent ocular opportunistic infection in AIDS patients. Untreated, it is always a progressive and destructive disease of the retina that results in blindness. Specific treatment is therefore mandatory to halt the progression of the retinal lesions. The authors report their experience in the treatment of CMV retinitis with foscarnet in 25 AIDS patients; the drug is an analog of pyrophosphate, virostatic against all herpes-class viruses including CMV. Foscarnet was successful in halting the progression of CMV retinitis during induction treatment (180 mg/kg/day) by either a TID (three times a day) or a BID (twice a day) regimen, and in healing retinal lesions during maintenance (90 mg/kg/day) in 14 out of 19 patients. Five patients had a relapse of retinitis during maintenance. In these patients a brief course of intravitreal foscarnet, in association with the lowest dosage of the drug administered systematically (90 mg/kg/day), was effective in healing the retinal lesions. The main systemic side effects, such as renal impairment and electrolytic disturbances, were observed only during the induction treatment, and only in one case was it necessary to stop the therapy.