The study is based on 122 trabeculectomies performed on eyes with open angle glaucoma (glaucoma simplex). Satisfactory control of intraocular pressure was achieved in 80 to 90 percent of the eyes. Refixation of the scleral flap into its bed with sutures is an essential feature of the operation. This provides a valve mechanism. As a rule the valve does not open postoperatively unless the intraocular pressure has again reconstituted itself to some extent. Clinical advantages are: 1. Generally the anterior chamber has normal depth at the first postoperative day. 2. Postoperative hypotony is rare. 3. Usually postoperative inflammation is of low degree and of short duration. 4. Short hospitalisation. At present trabeculectomy is the authors operation of choice in eyes with glaucoma simplex.