To report on visual outcome of patients receiving intravitreal triamcinolone acetonide for treatment of diffuse diabetic macular edema. Prospective, comparative clinical interventional study. Institutional. patient population: The study included 25 consecutive patients (50 eyes) with bilateral diabetic macular edema. Intervention procedure: Unilateral intravitreal injection of about 20 mg triamcinolone acetonide into the eye (study group) more severely affected by diabetic maculopathy. The contralateral eyes served as control group. Mean follow-up was 7.1 +/- 4.1 months. Visual acuity, intraocular pressure. In the study group, visual acuity increased significantly (P < or = .001) by 3.0 +/- 2.6 Snellen lines to a peak at two to six months after the injection, and decreased significantly (P = .001) towards the end of follow up. At the end of follow-up, visual acuity was higher, not significantly (P = .18) higher, than at baseline. An increase in visual acuity was found in 23 eyes (92%). In the control group, differences between visual acuity at baseline and at any of the re-examinations during follow-up were not significant (P > .10). In an intra-individual inter-eye comparison, gain in visual acuity was significantly (P < .05) higher in the injected eyes, for the measurements obtained up to four months after injection. Intravitreal triamcinolone acetonide may temporarily increase visual acuity in eyes with diabetic macular edema.