Doxorubicin is reported to cause myelosuppression, with a white blood cell count nadir occurring between day 7 and day 10. Thrombocytopenia is less severe and occurs between days 3 and 8. This report presents an early onset of leukopenia (day 5) and a severe thrombocytopenia (4000 platelets/microliter) (day 6) associated with doxorubicin administration for treatment of recurrent tonsillar squamous cell carcinoma in a dog.