In a critical review of trabeculectomy, some factors and steps that I consider important for its successful outcome are discussed. Trabeculectomy is a misnomer, because the success of this procedure does not depend on inclusion of trabecular meshwork or Schlemm's canal in the excised tissue. Furthermore, development of a conjunctival bleb is seen in most, if not all, eyes with successful trabeculectomy. Trabeculectomy is, then, a form of guarded filtering procedure. Several factors seem to determine the outcome of the final intraocular pressure control after trabeculectomy. In this study, intracameral air injection and gauging of the closure of the lamellar scleral flap according to an air test during trabeculectomy proved very useful in attaining optimal closure of the lamellar scleral flap. It was effective in preventing undesirable postoperative complications as well as in achieving a satisfactory success rate. Trabeculectomy, as reported by others, seems to be a remarkably successful and safe procedure. However, the results in aphakic glaucoma are disappointing. From all indications at the present time, trabeculectomy will stay with us as a primary procedure for open-angle and chronic angle-closure glaucomas in adult phakic eyes, although we do not yet know how many of the eyes with seemingly successful trabeculectomies will remain healthy in the future.