• PURPOSE: To analyze the effect of angiotensin-converting enzyme (ACE) inhibitor lisinopril on inflammatory cystoid macular edema and visual acuity. • DESIGN: Randomized, double-blind, placebo-controlled cross-over trial. • METHODS: setting: Outpatient clinic of the Department of Ophthalmology at the University Medical Center of Utrecht. Patients: Forty patients with inflammatory cystoid macular edema were included. intervention: Each patient received lisinopril (10 mg daily) or placebo for three months. After two months of a lisinopril/placebo free wash-out period, the groups received the reverse study medication for three months. Fluorescein angiography was performed to evaluate the retina. main outcome measures: Cystoid macular edema, best-corrected visual acuity and contrast sensitivity. • RESULTS: Lisinopril had no effect on cystoid macular edema, visual acuity, papillary leakage, retinal vasculitis, and choroidal leakage. In a subgroup analysis, we observed a decrease in blood pressure (lisinopril, 14 of 36 patients; placebo, 5 of 36 patients; P = .02) and a decrease in morning urinary albumin excretion (lisinopril, 23 of 35 patients; placebo 10 of 34 patients, P = .003) was observed. • CONCLUSIONS: Although lisinopril had no effect on inflammatory cystoid macular edema and visual acuity, we found a positive effect on the vascular system.