A 15-year old draft horse mare was presented to the University Clinic for evaluation of lethargy, anorexia, ptyalism, weight loss and ventral oedema. Clinical examination and rectal palpation revealed generalised lymphadenopathy and numerous firm subcutaneous and abdominal masses of various sizes. Transcutaneous ultrasonography revealed significant bilateral pleural fluid accumulation and a single hypoechoic structure in the abdomen lateral to the liver. Blood analysis showed several abnormalities including a marked leucocytosis with an increased number of segmented neutrophils, atypical lymphocytes and monocytosis, suggestive of leukaemic lymphoma. A significant hyperproteinaemia with a hypoalbuminemia and a monoclonal gammopathy was identified. At necropsy myriad masses presented through the whole body. Histology confirmed the suspicion of lymphoma, which was classified as a T-cell rich B-cell multicentric lymphoma. This article describes the clinical and pathologic findings of this case of leukaemic lymphoma.