Purpose: The purpose of this study was to evaluate the safety and efficacy of intravitreal triamcinolone acetonide injection in patients with diffuse diabetic macular edema. We also compared the effect of intravitreal triamcinolone with macular grid laser photocoagulation in macular edema. Patients and Methods: Thirty patients with diabetic diffuse macular edema unresponsive to grid laser photocoagulation for at least 4 months received 0.1 ml ( 4 mg/ml) intravitreal triamcinolone acetonide ( Kenakort-A) injection as treatment. This study group was compared with a control group of 30 patients ( 30 eyes) who had undergone grid laser macular coagulation. Mean follow-up time was 17 months ( range 14 - 24 months) in the study group and 19 months ( range 16 - 24 months) in the control group. Results: In the study group, mean improvement in visual acuity measured 3.8, 3.4, 0.9 and 0.2 Snellen lines at the follow-up intervals of 1, 3, 6 and 12 months, respectively. Improvement in visual acuity was statistically significant only at 1 month ( p = 0.002) and 3 months ( p = 0.003) after injection. Visual acuity was significantly ( p < 0.05) better in the study group than the control group at 1 and 3 months. Overall, 6 of 30 eyes ( 20%) required a second injection and 3 eyes ( 10%) a third due to regression in visual acuity. Towards the end of the follow-up period, the visual acuity decreased to almost baseline levels. Elevation of intraocular pressure was found in 4 patients and controlled with topical antiglaucomatosis treatment. Sterile endophthalmitis was detected in only one eye. No eye exhibited cataract progression during the follow-up period. Conclusion: Intravitreal injection of triamcinolone may be beneficial for temporarily increasing visual acuity in patients with diabetic diffuse macular edema who are unresponsive even to grid laser photocoagulation. But the regression of visual acuity looks inevitable in the long term after injection. Therefore, repeated injections with/without increasing doses might be required for the stabilization of visual acuity. Copyright (c) 2005 S. Karger AG, Basel.