Objective: This document describes endonasal dacryocystorhinostomy (DCR) and examines the evidence to answer key questions about the effectiveness of the procedure compared with external DCR; the relative indications, contraindications, advantages, and limitations of the procedure; and patient selection, surgical technique, postoperative care, and complications. Methods: A literature search conducted for the years 1968 to 2000 retrieved 93 citations. The panel members reviewed 71 of these articles and selected 64 for the panel methodologist to review and rate according to the strength of evidence. A level I rating is assigned to properly conducted, well-designed, randomized clinical trials; a level II rating is assigned to well-designed cohort and case-control studies; and a level III rating is assigned to case series and poorly designed prospective and retrospective studies, including case-control studies. Results: The published literature includes two reports that describe clinical trials comparing endonasal with external DCR with a 1-year follow-up. The success rate was 91% for the external DCR group in both reports and 63% and 75% for the endonasal DCR groups, defined by patency to irrigation. A longitudinal cohort study included a control group of age-matched external DCR patients who were compared with a study group of endonasal DCR patients. The reported success rate at 9 months following surgery for the endonasal cohort was 90% and was not statistically significantly different from the 94% success rate noted in the external DCR control group. Remaining data on reported success rates of primary and revision endonasal DCR were obtained from a collection of uncontrolled observational case studies with varying periods of follow-up and success rates ranging from 59% to 100%. Conclusions: It is difficult to make definite evidence-based determinations about the relative efficacy of endonasal and external DCR because of the deficiencies in the reported literature. Based on level III evidence, the available data suggest that endonasal DCR may be a viable option for the correction of acquired nasolacrimal duct obstruction and complex forms of congenital dacryostenosis in selected patients. This procedure may be indicated on a primary basis or as revisional surgery following failed external or endonasal DCR. Some studies comparing endonasal DCR with external DCR suggested lower success rates in the endonasal group; other studies yielded success rates comparable with or exceeding those of external surgery. Reported complications of endonasal DCR do not generally appear to be greater in frequency or magnitude than those associated with external DCR. Disadvantages of endonasal DCR include the preferred use of general anesthesia by many surgeons, the high cost of expensive equipment and instrumentation, and the relatively steep learning curve for this procedure. Depending on the preference of the surgeon, more postoperative care may be required for patients undergoing endonasal DCR than external DCR. Both the advantages and the limitations of endonasal DCR relative to external DCR should be carefully discussed with patients who are contemplating endonasal surgery.