Cutaneous mast cell tumors (MCTs) are among the most common neoplasms in dogs and show a highly variable biologic behavior. Histological grading, cell proliferation markers, and KIT immunohistochemistry are typically used to predict post-surgical prognosis. In the present study, c-KIT messenger RNA (mRNA) expression was measured in canine MCTs and its relationship with tumor grade, immunohistochemical staining pattern, post-surgical prognosis, and mutations was investigated. A significant increase of c-KIT mRNA was observed in MCTs versus healthy skin and surgical margins. Mutations were observed in 8.3% of cases. The KIT staining pattern was investigated for both grading systems. In particular, staining pattern III was associated with grade II (G2) and G3 MCTs, while staining patterns I and II were associated with G1 and G2 MCTs. Considering the 2-tier histological grading, the high grade was mainly associated with pattern III (71%) while the low grade was associated with patterns II (70%) and I (28%). A weak association between the KIT staining pattern and outcome was also observed. The results obtained suggest that c-KIT mRNA is overexpressed in canine MCT, although the fold variations were not associated with the protein localization or complementary DNA mutations. These observations suggested that the 3 events were independent. The histological grading and the KIT staining pattern have prognostic value as previously published. Staining pattern I could be especially helpful in predicting a good prognosis of G2 MCTs. Sequence mutations were not necessarily suggestive of a worse prognosis, but might be useful in choosing a chemotherapy protocol.