Four dogs presented with leukocytosis (range: 81,000–179,600 leukocytes/μL), no or moderate peripheral lymphadenopathy and an expanded population of small to intermediate CD3+CD5+CD8+MHCII+ lymphocytes on blood FCM, compatible with T cell chronic lymphocytic leukemia (T-CLL). The gene discussed is CD5; the disease is Lymphadenopathy.