The objective of the present study was to evaluate the diagnostic interest of cytological analysis in canine mammary tumours. A total of 100 canine mammary tumours histologically analysed and classified into malignant (76%), benign (19%) and dysplastic changes (5%) were also cytologically analysed by impression method and 2 staining (Papanicolaou (PAP) and May-Grunwald-Giemsa (MGG)) methods. The total agreement scores between histopathology and cytological analysis using PAP and MGG staining methods were 88% and 86% respectively (the percentages of false negative and false positive samples being 2% and 7% with PAP and 3% and 10% with MGG). Among the malignancy criteria, those with major cytological interest were pleomorphism, large nuclei, nuclear membrane alterations, variable nucleolar size, shape and quantity, coarse chromatin and hypercellularity whereas others (high nucleus / cytoplasmic ratio, mitotic index, nuclear and cytoplasmic vacuolisation, presence of giant cells, spindle cells, pseudosyncytial clusters, squamous epithelial cells, leukocyte infiltration and necrotic debris at a lesser extend) highly relevant for histopathological analysis cannot be valuable criteria for cytology because of their infrequency in cytological impression samples. These results show that cytological evaluation of canine mammary tumours may constitute however a rapid and relevant way to malignancy diagnosis according to the retained malignancy criteria.