An adult female spayed Golden Retriever previously diagnosed with lymphoblastic lymphoma was presented to the Iowa State University oncology service with severe thrombocytopenia (20,000 plts/μL, reference interval: 200,000-500,000 plts/μL). Through bone marrow aspiration and cytology, it was found that the patient’s megakaryocytes demonstrated marked anisocytosis, cytosolic hypogranulation, and nuclear hypolobulation, which are all abnormal morphological findings consistent with dysmegakaryocytopoiesis, a type of myelodysplastic syndrome. The myelodysplastic syndromes refer to a collection of conditions characterized by the dysplasia of one or more of the hematopoietic cell lineages. Primary myelodysplastic syndromes are idiopathic, whereas secondary myelodysplastic syndromes have been associated with infectious diseases, toxin exposure, and drug treatments, including chemotherapy. Specifically, cancer patients receiving high cumulative doses of antineoplastic agents may be at an increased risk of developing a secondary myelodysplastic syndrome. At the time of diagnosis of dysmegakaryocytopoiesis, the patient had received 33 doses of chemotherapy through a University of Wisconsin-Madison multidrug protocol for canine lymphoma. Due to this development, it was elected to suspend the patient’s chemotherapy and the dysmegakaryocytopoiesis resolved within 2 months. The fact that cessation of chemotherapy was sufficient in increasing the patient’s platelet count into the normal range, and that the patient had no evidence of any additional underlying predisposing diseases or exposures, suggests that the cumulative cytotoxic effects of the chemotherapy treatment led to the development of dysmegakaryocytopoiesis. To our knowledge, this is only the second report in the veterinary literature describing chemotherapy-induced selective dysmegakaryocytopoiesis.