Gray zone lymphoma (GZL) is defined as a B-cell lymphoma with intermediate features between both diffuse large B-cell lymphoma (DLBCL) and classical Hodgkin lymphoma (CHL). GZL is an aggressive disease, which in addition to the B-symptoms, can present as shortness of breath and neck swelling from underlying superior vena cava (SVC) syndrome. Thrombosis of the internal jugular vein (IJVT) is rare and usually associated with head and neck infection, intravenous (IV) drug abuse, and central venous catheter placement. GZL's initial presentation as IJVT with SVC syndrome is very uncommon. We report the case of a 47-year-old female presenting with neck swelling and shortness of breath. Initial investigations were oriented at the thyroid gland. A computerized tomography (CT) scan of the chest, neck, and head showed a large anterior/superior mediastinal soft tissue mass with left IJVT. An excisional biopsy of the left axillary lymph node confirmed the diagnosis of GZL. The mediastinal lymphoma can compress the internal jugular vein and also release thrombogenic substances that can cause IJVT. The compression of the SVC by the lymphoma and the IJVT formation can cause SVC syndrome. Both of these conditions can be lifethreatening and should be identified in the early stages to prevent complications.