A four year old, male castrated, mixed breed dog was evaluated for a five day history of inappetence, polyuria and polydipsia. Initial physical exam and diagnostic findings included 5% dehydration, bilaterally enlarged popliteal lymph nodes, elevated ionized calcium and azotemia. Diagnostic testing ruled out all causes of hypercalcemia, except humoral hypercalcemia of malignancy. Aspiration of the popliteal lymph nodes revealed lymphoid hyperplasia indicative of antigenic stimulation, however lymphoma could not be ruled out. A bone marrow aspirate was suggestive of, but not definitive for, small cell lymphoma, so a PCR Antigen Receptor Rearrangment (PARR) was submitted. The results were equivocal, but suggestive for a clonal expansion of T-cells. The owner declined chemotherapy and instead elected prednisone treatment. Based on the patient’s marked clinical improvement after steroid administration, and cytologic and immunocytologic results being suggestive of lymphoma, a presumptive diagnosis of Stage V, T-cell Lymphoma, substage b was made.