The case of a 72-year-old woman with diffuse large B-cell lymphoma of the lacrimal sac is reported. The patient was evaluated for the first time in our department for tearing of the right eye. One month later, a slightly aching mass appeared over the right lacrimal sac. An acute infectious etiology was suspected and antibiotic therapy was given. When she finally presented with a rapidly growing lesion, she underwent echography and computed tomography followed by incisional biopsy. Results of histopathologic and immunohistochemical evaluation showed a primary, diffuse, large B-cell non-Hodgkin lymphoma of the lacrimal sac. This case demonstrates how difficult the clinical diagnosis of tumors of the lacrimal sac may be in the early stages. The clinical signs, usually aspecific, may be misleading and the diagnosis delayed.