Intra-thoracic tumours are a heterogeneous group of neoplastic diseases in both humans and dogs. They are often difficult to diagnose because of their non-specific clinical signs and their deep location. The hypothesis of an intra-thoracic tumour requires the use of medical imaging techniques, pathological examination or even exploratory surgery to be confirmed. Once the diagnosis of an intratheacal tumour and the extension work-up are established, the prognosis and treatment strategy can be deduced. The aim of this paper is to provide a better understanding of these conditions and to outline the diagnostic and therapeutic approaches in dogs and humans. The treatment of these tumours is multidisciplinary, often involving surgery, chemotherapy, radiotherapy and other new therapeutic modalities, including targeted therapies and immunotherapy.