Tear production resulting from obstruction of the nasolacrimal duct is a common ophthalmic problem. The diagnosis and treatment of this condition require a thorough understanding of the lacrimal apparatus and its ocular and nasal relationships. Idiopathic or primary acquired nasolacrimal duct obstruction is a syndrome of unknown etiology. Of all nontraumatic forms, it accounts for the vast majority of cases found in adults. The authors discuss a number of potential causes, some of them iatrogenic and discuss the technique of dacryocystorhinostomy, the standard surgical treatment, in detail.