Ketorolac tromethamine 0.5% ophthalmic solution treatment was compared to placebo treatment in 120 patients with chronic aphakic or pseudophakic cystoid macular edema (six-month or more duration of distance visual acuity of 20/40 or less and angiographic evidence of cystoid changes) during a four- to five-month double-masked, multicenter study in which patients were randomly assigned. A statistically significant improvement in distance visual acuity (two lines or more) was observed in the ketorolac-treated group as compared to the placebo-treated group after 30 days (P = .038), 60 days (P = .017), and 90 days (P = .008) of treatment. This improvement in visual acuity remained statistically significant one month after cessation of treatment (P = .001). Nine ketorolac-treated patients and two placebo-treated patients demonstrated a decrease in visual acuity one month after treatment was discontinued. Seven of the nine ketorolac-treated patients experienced an improvement in visual acuity after retreatment as compared to none of the placebo-treated patients. This study offers evidence for a more optimistic outlook in the medical treatment of chronic aphakic and pseudophakic cystoid macular edema.