Canine immune-mediated thrombocytopenia (IMT) is a potentially fatal disease mediated by platelet-bound antibodies that initiate destruction of platelets by the mononuclear phagocytic system. IMT may be classified as a primary condition, for which there is no apparent inciting cause for platelet destruction, or as a secondary condition, in which a primary disease process precipitates immune-mediated platelet destruction. Diagnosis of primary IMT is made by documentation of severe thrombocytopenia in the absence of an obvious infectious or neoplastic process, and response to immunosuppressive therapy. Traditionally, treatment has consisted of the administration of glucocorticoids, with or without co-administration of additional immunosuppressive drugs, most commonly azathioprine. Use of other immunosuppressive treatments, among them vincristine and human immunoglobulin G, have also been reported. The use of mycophenolate mofetil as an adjunct treatment has not been reported. Administration of platelet transfusions for IMT is controversial, as transfused platelets have a short survival time and questionable functionality.