A 6 year old female intact Savannah cat presented to the Cornell University Hospital for Animals Emergency Service in September 2008 for severe respiratory distress. Initial diagnostics indicated the presence of a large cranial mediastinal mass. An ELISA snap test for FeLV came back as positive, and an ultrasound guided aspirate of the mass was comprised mostly of intermediate to large sized lymphocytes. Due to these findings, an initial diagnosis of mediastinal lymphoma was made. At this point further diagnostic tests were declined, the patient was euthanized and a necropsy was performed. Upon histopathologic examination of the mass, it was concluded the mass was in fact a lymphocytic predominant thymoma, due to the predominance of small hyperchromatic lymphocytes with clusters of epithelial cells and rare Hassal's corpuscles. This case highlights the difficulty in differentiating mediastinal lymphoma and thymoma, and the need to make a definitive diagnosis based on biopsy before formulating prognoses or treatment plans.