AIM:To compare therapeutic effects of intravitreal triamcinolone acetonide (IVTA) versus intravitreal bevacizumab (IVB) injections for bilateral diffuse diabetic macular edema (DDME).METHODS: Forty eyes of 20 patients with bilateral DDME participated in this study. For each patient, 4 mg/0.1 mL IVTA was injected to one eye and 2.5 mg/0.1 mL IVB was injected to the other eye. The effects of injection for diabetic macular edema (DME) were evaluated using best-corrected visual acuity (BCVA), central macular thickness (CMT) by optical coherence tomography (OCT) and intraocular pressure (IOP) by applanation tonometer. Patients underwent eye examinations, including BCVA, CMT, and IOP at pre-injection, 1, 4, 8, 12 and 24wk after injection. During the follow-up, second injections were performed to eyes which have CMT greater than 400 μm at 12wk for salvage therapy.RESULTS: BCVA (logarithm of the minimum angle of resolution) at pre-injection, 1, 4, 8, 12 and 24wk after injection was 0.71±0.19, 0.62±0.23, 0.63±0.12, 0.63±0.13, 0.63±0.14 and 0.61±0.24 in the IVTA group and 0.68±0.25, 0.61±0.22, 0.60±0.24, 0.62±0.25, 0.65±0.26 and 0.59±0.25 in the IVB group, respectively. CMT (μm) at pre-injection, 1, 4, 8, 12 and 24wk after injection was 544±125, 383±96, 335±87, 323±87, 333±92, 335±61 in the IVTA group and 514±100, 431±86, 428±107, 442±106, 478±112, 430±88 in the IVB group respectively. Reduction ratios of mean CMT were 29% at 1wk, 38% at 4wk, 40% at 8wk, 38% at 12wk, and 38% at 24wk in the IVTA group. Second IVTA injections were performed to the 6 eyes (30%) at 12wk. Reduction ratios of mean CMT were 16% at 1wk, 17% at 4wk, 14% at 8wk, 7% at 12wk, and 16% at 24wk in the IVB group. Second IVB injections were performed to the 15 eyes (75%) at 12wk.CONCLUSION:This study showed earlier and more frequent macular edema recurrences in the eyes treated with bevacizumab compared with the ones treated with triamcinolone acetonide. Triamcinolone acetonide was found to provide more efficient and long-standing effect in terms of reducing CMT compared with the bevacizumab.