A 36-year-old male patient presented with a firm swelling in the left lacrimal sac region with a history of recurrent episodes of acute dacryocystitis, which partly resolved with systemic antibiotics. Computed tomography showed diffuse soft tissue mass without bony erosion in the same area. Incisional biopsy confirmed diffuse large cell lymphoma of non-Hodgkin's type by histopathology and immunohistochemistry. Oncologists did not detect systemic involvement, and the patient received six cycles of cyclophosphamide, hydroxydaunorubicin, oncovin, and prednisolone (CHOP). Epiphora was resolved, and no recurrence of the lesion was seen with subsequent dacryocystorhinostomy with intubation and was in good health for up to 3 years of follow-up. Although primary lacrimal sac lymphoma is a rare entity, high suspicion, and prompt action in atypical cases can save lives from aggressive diffuse large cell lymphoma.