Purpose: Treatment of diffuse macular edema in diabetes mellitus is currently unsatisfactory. The purpose of this double blind randomized clinical trial was to compare the treatment of diffuse diabetic macular edema with intravitreal triamcinolone or laser in type 2 diabetes mellitus patients using a morphofunctional assessment. Methods: Fourteen patients (21 eyes) with clinically significant diffuse macular-edema, previously untreated and with a macular thickness >250 μm at optical coherence tomography were randomized for treatment with laser or intravitreal injection of triamcinolone acetate. Optical coherence tomography, biomicroscopy, fundoscopy, fluorescein angiography, tonometry, scotometry, visual and contrast acuities were performed at 0, 1, 3 and 6 months. Results: At pre-treatment stage, Laser (n=9) and Triamcinolone (n=12) groups did not differ regarding retinal thickness, visual and contrast acuities. In Triamcinolone group macular thickness decreased after 1 month (424.1 ± 19.9 μm to 358.4 ± 18.2 μm; p=0.04) and started to return to the initial values in the 3 rd month (p=0.02). No changes occurred in macular scotometry and visual and contrast acuities. No side effects were observed with both treatments. Conclusion: During the study macular thickness diminished in the triamcinolone group, especially in the first month of treatment. At 3 and 6 months there was no difference. Macular thickness did not change during the study in the laser group. In the study sample it was not possible to demonstrate differences relates to visual acuity and scotometry between the two groups. ClinicalTrials.