A retrospective study of canine and feline pancytopenia presumably due to immune-mediated destruction of blood cell precursors in bone marrow was conducted to characterize the clinical signs, laboratory test results, treatment and outcome of this condition. CUHA case records between 1994-2004 were reviewed and animals were included in the study if they fulfilled the following criteria: several days history of pancytopenia, hyperplasia of one or more cell lines in the bone marrow, absence of morphologic abnormalities in bone marrow precursors, no evidence of peripheral destruction, and no known underlying disease or drug therapy that could have caused the pancytopenia. Seven canine and 4 feline cases were included. Animals were generally young and female, and exhibited vague clinical signs such as lethargy and anorexia. Bone marrow aspirates were hypercellular with erythroid hypoplasia in dogs and erythroid hyperplasia in cats. Both responded well to immunosuppressive therapy over days to weeks. Therefore, an innume-mediated pathogenesis should be considered for dogs and cats presenting with pancytopenia due to ineffective hematopoiesis.