BACKGROUND: To analyse the inocuity and the incidence of complications of a 0.2 mg/ml solution of Mitomycin C (M.M.C.), for two application time, 2.5 or 5 minutes. METHODS: 110 trabeculectomies were realised in 99 patients; they were high-risk (HR) patients in 66 cases, and low-risk (LR) patients in 44 cases. M.M.C. was used for 2.5 minutes in 44 cases (20 HR patients, 24 LR patients), and for 5 minutes in 66 cases (46 HR patients, 20 LR patients). RESULTS: In both groups HR and LR, there is no significant difference on the pressure lowering whether the 0.2 mg/ml solution of M.M.C. is used during 2.5 minutes or 5 minutes (Student t-test at 6 months: HR: p = 0.224; FR: p = 0.542). For the early and late complication in the HR group, there is no significant difference whether M.M.C. is used 2.5 or 5 minutes. In the LR group, there is a significant difference for hypothalamy (p = 0.035) and choroidal detachment (p = 0.027). In this LR group, there is no significant difference in the late complications. CONCLUSIONS: A 0.2 mg/ml solution of M.M.C., when indicated, may be used as well in the HR and LR group during 2'30". In the HR group, if there are several risk factors, we propose to adapt the application time between 2.5 and 5 minutes, and increase it by 1/2 or 1 minute for each risk factor.