Topical application of mitomycin C has significantly increased the success rate of trabeculectomy. However the optimum exposure time of mitomycin C to the filtration site is not known. . The purpose of this study was to determine whether adequate post-operative control of IOP and a lower incidence of post operative complications can be achieved by using mitomycin-C for a shorter period of time during trabeculectomy, performed in high risk glaucoma patients. Methods: Twenty eyes of patients of glaucoma, who were considered to be at high risk for failure because of their young age, previous ocular surgery like cataract extraction and trabeculectomy, inflammatory glaucoma, high myopia and prolonged anti-glaucoma medication, underwent trabeculectomy with topical application of 0.2mg/ml concentration of mitomycin C for three minutes. They were case matched with a group of same number of eyes of high risk glaucoma patients who received same concentration of drug for 5 minutes. Results: Twelve months after surg ery, the mean pre-operative IOP decreased from 29.9mmHg to a post-operative level of 16.05mmHg in 3 minutes group, with a success rate of 85%, and from 29.35mmHg to 16.55mmHg in 5 minutes group, with the same success rate of 85%. The incidence of complications was higher in 5 minutes group, when total number of complications was compared. ( p value