Most patients with nasolacrimal duct obstruction present with tearing. The tearing may be unilateral or bilateral, constant or intermittent. The tearing patient may complain of visual blur from an increased tear meniscus and/or epiphora. Mattering or crusting of the eyelid margins is a sign of chronic infection and may also accompany obstructions of the lacrimal drainage system. The retained mucus and cellular debris in the nasolacrimal sac of an obstructed lacrimal system often can be expressed by pressure over the sac and the medial canthus. If obstructions prevent the emptying of the nasolacrimal duct distally and the common canaliculus proximally, a mucocoele or mucopyocoele of the nasolacrimal sac may result. A red, tender mass below the medial canthal tendon is indicative of an acute dacryocystitis and requires the immediate institution of systemic antibiotic therapy, or possibly surgical therapy, to bring about resolution. Tearing caused by an obstruction of the lacrimal drainage apparatus should be distinguished from excess lacrimation. Careful examination of the eye and ocular adnexa is necessary to exclude causes of excess tear production. Eyelid malpositions, trichiasis, inflammatory eyelid margin disease, ocular surface disease, tear deficiency or instability, and irritation of the trigeminal nerve may stimulate tear production. When these causes of excess lacrimation are not present and tearing caused by punctal malposition, lid laxity (lacrimal pump), or incomplete blink has been excluded, acquired obstruction of the lacrimal drainage system is the most probable cause. This report reviews the proper examination of a patient with suspected lacrimal outflow obstruction, with an emphasis on identifying the patient with obstruction of the nasolacrimal duct; the etiology of primary and secondary nasolacrimal duct obstruction; and, finally, current trends in medical and surgical therapy of acquired nasolacrimal duct obstruction.