We used the monochromatic green argon laser to treat 41 eyes with retinal branch vein occlusion (RBVO) and decreased vision because of chronic macular edema of at least six months duration after the onset of RBVO. The average follow-up period after treatment was 19 months. Cystoid macular edema (CME) occurred in 34 eyes and noncystoid macular edema in seven eyes. In eyes with chronic CME we decreased intracapillary pressure in the portion of the macula drained by the occluded vein by segmental retinal arteriolar narrowing using photocoagulation to the retinal arterioles that perfused the involved portion of the macula. Partial or complete resolution of macular edema occurred in 27 eyes. Vision improved in 19 eyes and was stabilized in seven eyes. In eyes with chronic noncystoid macular edema treatment consisted of focal closure of leaking microaneurysms and retinal telangiectasias with photocoagulation. Closure of these leaking vessels associated with partial or complete resorption of hard exudates that had accumulated in the macula secondary to the leakage occurred in six of the seven photocoagulated eyes. Vision improved in four eyes and was stabilized in two eyes.