Primary mediastinal B-cell lymphoma is believed to arise from a small population of thymic medullary B-cells, and is considered a distinct entity from diffuse large B-cell lymphoma, based on its unique clinical, histopathologic, and molecular features. It represents 2% of all non-Hodgkin lymphomas, and has a propensity to affect young women with a median age of 35 years. It usually presents with a bulky tumor in the anterior mediastinum that is rapidly progressive, causing local compressive symptoms. Although distant spread is infrequent at presentation, this subtype of lymphoma tends to spread to unusual extranodal sites such as liver, kidneys, and central nervous system. We present 2 cases of histologically proven primary mediastinal B-cell lymphoma, which demonstrate this pattern of distant spread to organs including the stomach and pancreas. In these cases, F-18 FDG PET-CT proved very useful in the evaluation of distant spread of the disease.