Lymphoproliferative disorders are a highly heterogeneous group of diseases that arise from different stages of lymphocyte development and have widely variable clinical outcomes. The goal of this session is to provide the audience with an understanding of the biological and clinical behavior of a range of canine lymphoproliferative disorders. The emphasis of the session will be on the most efficient and clinically useful method of diagnosis and classification. The advantages and limitations of cytology, histology and immunohistochemistry, clonality testing and flow cytometry will be presented. While our understanding of feline lymphoproliferative disorders is less well developed than in dogs, feline small cell intestinal lymphoma has been the focus of intense research recently. Methods for diagnosing this disease and controversies around those methods will also be presented.