Mast cell tumors represent the most common malignant skin tumor in the dog. This review outlines the incidence, etiology and clinical signs of mast cell tumors. Diagnostic tests, staging and treatments are also discussed. This study was performed by the Veterinary Oncology and Pathology of UNESP, Jaboticabal and the Service of Pathology Veterinary, of UNESP-Botucatu with the support of the Brazilian Association of Veterinary Oncology and the Brazilian Association of Veterinary Pathology.