We compared early postoperative complications between trabeculectomy and Ex-PRESS implantation. Enrolled patients with 39 primary open-angle or 25 exfoliative glaucoma were randomly assigned to receive trabeculectomy (trabeculectomy group) or Ex-PRESS implantation (Ex-PRESS group). Primary outcomes were early postoperative complications, including postoperative anterior chamber inflammation, frequencies of hyphema, flat anterior chamber, choroidal detachment, hypotonic maculopathy, and the change of visual acuity. The postoperative flare values in trabeculectomy group were higher than those in the Ex-PRESS group (overall, P = 0.004; and 10 days, P = 0.02). Hyphema occurred significantly more frequently in the trabeculectomy group (P = 0.0025). There were no significant differences of the other primary outcomes between the two groups. Additionally, duration of anterior chamber opening was significantly shorter in the Ex-PRESS group (P = 0.0002) and the eyes that had iris contact with Ex-PRESS tube had significantly shallower anterior chambers than did the eyes without the iris contact (P = 0.013). The Ex-PRESS implantation prevented early postoperative inflammation and hyphema in the anterior chamber and shortened the duration of anterior chamber opening. Iris contact with the Ex-PRESS tube occurred more frequently in eyes with open-angle glaucoma and shallow anterior chambers.