Background: We investigated in a prospective fashion the visual prognosis and complications in normal-tension glaucoma following unilateral trabeculectomy with adjunctive mitomycin C. Methods: Trabeculectomy with adjunctive mitomycin C was carried out unilaterally in 21 cases of normal-tension glaucoma. Intraocular pressure (IOP), visual prognosis, and complications were compared between the operated eyes and the non-operated fellow eyes. The follow-up period ranged from 2 to 7 years. Results: The IOP dropped significantly from 14.8±1.8 mmHg (mean ± SD) to 9.6±3.9 mmHg in the operated eyes (P=0.0002, Wilcoxon signed-rank test ), but did not drop in the non-operated eyes. The mean deviation (MD) was –12.69±6.41 dB preoperatively and –14.70±5.49 dB at the last clinic visit in the operated eyes, whereas in non-operated eyes it was –7.85±5.65 dB and –11.15± 5.62 dB, respectively. The MD deteriorated significantly in both operated and non-operated eyes (operated eyes P=0.0239, non-operated eyes: P=0.0002; Wilcoxon signed- rank test). The MD slope was –0.37±0.60 dB/year and –0.71± 0.89 dB/year for the operated and non-operated eyes, respectively (P=0.5243, Mann-Whitney U-test). Visual field deterioration was more frequently observed in the non- operated eyes by a pointwise definition of the progression (P<0.05, McNemar test). Visual acuity deteriorated in 6 of the operated eyes and in 5 of the non-operated eyes. Cataract developed in 6 (29%) of the 21 operated eyes, while among the non-operated eyes 4 (19%) developed cataract. Conclusion: Mitomycin C trabeculectomy is effective in delaying progression of visual field defect in normal-tension glaucoma, but complications may arise and cause some visual disturbance.