Feline patients with unexplained peripheral blood cytopenias, circulating immature or neoplastic cells, dysplastic or dysmorphic bone marrow abnormalities, and/or lymphoid tumors are likely suffering from an underlying retroviral infection with feline leukemia virus (FeLV) and/or feline immunodeficiency virus (FIV). Cytopenic hematologic disorders are often caused by the direct or indirect hematosuppressive effects of these retroviruses. Alternatively, secondary infections, nutritional deficiencies, and/or hematopoietic neoplasms may be important cofactors in the development of blood and bone marrow abnormalities in retrovirus-positive patients. Mild to moderate nonregenerative anemia, with or without concurrent granulocytopenia and/or thrombocytopenia, is one of the most frequent hematologic disorders encountered with either infectious agent. Severe, isolated anemia with absent reticulocytes (pure red blood cell aplasia) specifically suggests infection with FeLV subgroup C. Hemolytic (regenerative) anemia, more commonly associated with FeLV infection, may be caused by an autoimmune process and/or coinfection with Haemobartonella felis. Lymphopenia is a hallmark of chronic, symptomatic FIV infection. Neutropenia may accompany a panleukopenia-like syndrome in FeLV-positive cats or it may be associated with acute primary infection or an adverse drug effect in the FIV-infected patient. FeLV and, to a lesser extent, FIV are both causally related to lymphoid neoplasms in domestic cats, but with dissimilar epidemiologic, clinical, and host cell phenotypic features. Clinicians must be cognizant of the wide spectrum of hematologic manifestations of FeLV and FIV infections to recognize and appropriately manage these complications in their feline patients.