PURPOSE. To report on the follow-up of patients who received an intravitreal high-dosage injection of triamcinolone acetonide (IVTA) as treatment of diffuse diabetic macular edema. METHODS. The clinical interventional case-series study included 109 eyes (90 patients) with diffuse diabetic macular edema who consecutively received an IVTA of about 20 mg. Mean follow-up was 11.2 +/- 6.2 months. RESULTS. Visual acuity improved significantly (p<0.001) from 0.89 +/- 0.33 logMAR to a best minimum of 0.65 +/- 0.35 logMAR. An increase in best visual acuity by at least 1 Snellen line, 2 lines, and 3 lines was found in 91 (83%) eyes, 68 (62%) eyes, and 45 (41%) eyes, respectively. Differences in visual acuity between baseline and follow-up examinations were significant for measurements performed at 1 month (p<0.001), 2 months (p<0.001), 3 months (p<0.001), and at 6 months (p=0.001) after the injection. At 9 months after the injection, mean visual acuity regressed significantly so that visual acuity at 9 months (p=0.83) and at 12 months after the injection (p=0.58) compared with baseline values did not differ significantly. Forty-seven (43%) eyes developed a rise in intraocular pressure (pressure > 21 mmHg) for 6 to 8 months after the injection. No other severe complications were detected. CONCLUSIONS. The duration of a visual acuity increase and intraocular pressure rise after high-dosage IVTA in diffuse diabetic macular edema is about 6 to 8 months. Compared with data in the literature, the high-dosage IVTA may not have a markedly higher profile of side effects than low-dosage IVTA. (Eur J Ophthalmol 2006; 16: 566-72)