In this study, the effect of subconjunctival retention of perfluoropropane (C3F8) gas on trabeculectomy was evaluated to determine if this maneuver would increase the success rate of the surgery. Thirty-two patients (under 35 years old) with a diagnosis of primary open-angle glaucoma or steroid-induced glaucoma were randomized into two groups to receive trabeculectomy: Group A (trabeculectomy alone, 16 eyes) and Group B (trabeculectomy with subconjunctival retention of 0.5 mL pure C3F8 gas, 16 eyes). The results showed that the typical appearance of a subconjunctivally retained C3F8 filtering bleb is highly distended in the first two weeks after surgery, followed by flattening and diffusing gradually. The average retention time of C3F8 gas within the subconjunctival space is 28 +/- 6 days. A higher success rate was noted in Group B than in Group A (94% versus 50%, p = 0.016) at a mean follow-up time of 12 months. However, there were no differences in complication rates and results of final visual acuity between the two groups (both groups had two patients lose more than two lines of vision, p = 1.0). Our study suggests that subconjunctival retention of C3F8 gas increases the success rate of trabeculectomy in young people in the intermediate-term (12 months) follow-up period.