Mast cell tumors are one of the most common occurring cutaneous and subcutaneous tumors in the canine. Their appearance is extremely variable making fine needle aspiration imperative for pre-surgical diagnosis. Diff-Quick staining is usually sufficient to expose the cytoplasmic granules, however, occasionally Giemsa or Wrights stain is needed. The most widely accepted method of treatment is surgical excision with three centimeter lateral margins and one fascial plane deep. This may or may not be followed up by radiation depending on the grade and margin detemination (clean or dirty). Mast cell tumors are broken down into a histologic grade ranging from one to three. Most canine mast cell tumors are histologically characterized as a grade II (40%). The behavior of a grade II mast cell tumor can range from benign (grade I) to highly metastatic (grade III). Due to the extreme inconsistency in biologic behavior of grade II mast cell tumors it is imperative that a more superior prognostic indicator be found. According to one study, the c-kit receptor protein expression on the mast cell is a useful method for fine tuning the prognosis of grade II mast cell tumors. The case study of a ten year old female spayed golden retriever will illustrate one process of diagnosis, treatment and prognosis of grade II mast cell tumors in a canine.