Tumors originating from the lacrimal sac are exceedingly rare. They may mimic chronic inflammation and be misdiagnosed, delaying treatment and allowing the tumor to devastate the visual system. Mucoepidermoid carcinoma has been described only occasionally. We report a case that presented with unusual diagnostic and treatment aspects. A 33-year-old Italian man had tearing in his right eye. The initial presentation mimicked dacryocystitis, and the patient had been treated with antibiotics and steroids, without results. Consequently, an external dacryocystorhinostomy was performed, during which an open biopsy specimen was taken; it suggested the presence of a basocellular epithelioma. Computed tomography, magnetic resonance imaging, and further biopsies led to the diagnosis of squamous carcinoma of the lacrimal sac. On this basis, the patient underwent preoperative radiation (41.4 Gy) and conservative surgical resection of the tumor, with preservation of the eye and extraocular muscles. The histopathologic examination of the gross surgical specimen led to a final diagnosis of primary mucoepidermoid carcinoma of the lacrimal sac and revealed clear resection margins. The clinical evaluation and positron emission tomography at 6 months showed complete functional recovery and no evidence of the disease. This report highlights the clinicopathologic characteristics and therapeutic uncertainty of this rare tumor.