A 50-year-old woman presented with a 5-year history of unilateral epiphora that began shortly after 131I therapy for thyroid carcinoma. A recent recombinant human thyroid-stimulating hormone (Thyrogen) scan had shown a focus of uptake adjacent to the right eye that was initially thought to be a possible metastasis. Probing and irrigation revealed complete blockage of the right nasolacrimal duct. The patient underwent a right dacryocystorhinostomy (DCR) and biopsy of the lacrimal sac. Histopathologic examination of the lacrimal sac and nasal mucosa revealed foreign-body reaction and fibrosis with no malignant cells. A repeat Thyrogen scan after DCR showed no residual focus of activity in the nose or near the lacrimal sac and confirmed reestablishment of lacrimal drainage on the right side. This case demonstrates that 131I therapy for thyroid carcinoma can be associated with nasolacrimal duct obstruction. The appearance of a focus of uptake near the lacrimal sac on Thyrogen scanning in a patient with a history of thyroid carcinoma may not be due to a new focus of metastasis and may indeed be due to pooling of 131I in the lacrimal sac due to nasolacrimal duct blockage.