BACKGROUND Primary pulmonary diffuse large B cell lymphoma (DLBCL) is extremely rare neoplasm representing only 0.5-1% of primary pulmonary malignancies. These patients usually have non-specific clinical presentation and radiological findings. Therefore, it is important to increase awareness of this rare disease, as the correct characterization of the tumors will have therapeutic and prognostic implications. CASE REPORT We present the case of a middle-aged Hispanic woman with chronic cough and an abnormal chest X-ray revealing a lung mass, who was found to have primary pulmonary DLBCL. She underwent 6 cycles of R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone) therapy and attained complete remission. CONCLUSIONS With its non-specific presentation, the diagnosis of primary pulmonary DLBCL is very challenging and often leads to misdiagnosis or delayed diagnosis. The pathogenesis of primary pulmonary DLBCL is still poorly understood. The choice of treatment approach should be based on the biological characteristic of the tumor, stage, and performance status.