Introduction: Canine transmissible venereal tumour is occasionally observed in leishmaniotic dogs, and Leishmania amastigotes can be harboured in canine transmissible venereal tumour cells.

Objectives: The aim of this paper was to investigate the clinicopathological significance of the association of both diseases.

Methods: Nineteen dogs affected by canine transmissible venereal tumour and canine leishmaniasis were studied retrospectively.

Results: In these dogs, the tumour manifested a large size and often aggressive behaviour (42%) and no predictive sign of spontaneous regression was observed. Sporadic Leishmania amastigotes were found within the canine transmissible venereal tumour in three cases, probably transported by infected macrophages often infiltrating the tumour. A high Leishmania parasitisation of canine transmissible venereal tumour was observed in two other cases and verified by immunohistochemistry.

Clinical Significance: Canine transmissible venereal tumour is a tumour of the dog able to harbour a large number of Leishmania parasites. Alternatively, the systemic disease (canine leishmaniasis) may lower the immune defence against malignancy (canine transmissible venereal tumour).