Diffuse large B-cell lymphoma originating from the maxillary sinus is rarely reported in the literature. Diagnosis is challenging since the long absence of signs and symptoms allows it to grow undetected or be confused with benign inflammatory conditions. The purpose of this paper is to present an unusual manifestation of this rare pathology. A patient in his 50s, presented to his local emergency department with malar and left eye pain after local trauma. Physical examination showed infraorbital edema, palpebral ptosis, exophthalmos, and left ophthalmoplegia. CT scan showed a soft tissue mass measuring 43x31 mm in the left maxillary sinus. An incisional biopsy was performed, and results showed diffuse large B-cell lymphoma with positivity for CD10+, BCL6+, BCL2+, and Ki-67 index greater than 95%. Afterward, the patient promptly started treatment with rituximab-cyclophosphamide-hydroxydaunorubicin-Oncovin-prednisone (R-CHOP) chemotherapy. A good medical history, clinical and imaging evaluations, and anatomopathological studies are crucial to establish an early diagnosis of diffuse large B-cell lymphoma (DLBCL).