A 4-year-old intact, female, Boxer dog was presented for a 3-month history of nonpruritic nodule on the right hind limb. Dermoscopy with polarized light was made, and a non-pigmented lesion with a reddish colour at the periphery, yellowish central area with chrysalis, thin telangiectasias in the reticular vascular pattern and polymorphic vessels surrounding the homogeneous area was observed. Later, cytological examination was performed, and a presumptive diagnosis of mast cell tumour was ascribed. An excisional biopsy of the nodule was taken, and histopathological examination confirmed the diagnosis of cutaneous mast cell tumour. To the best of the authors' knowledge, this is the first report of dermoscopy of cutaneous mast cell tumour in dogs. F I G U R E  Clinical presentation of cutaneous mast cell tumour in a dog. (a) Nodular lesion on the right pelvic limb measuring approximately 1.2 × 0.9 cm diameter. (b) A closer view of the lesion revealing an erythematous background