A 13-year-old female neutered domestic longhair cat was presented for intermittent, selflimiting episodes of laboured breathing and wheezing and also vocalising, coughing, retching, vomiting and inappetence. Abdominal ultrasound and thoracic radiographs revealed a peritoneopericardial diaphragmatic hernia (PPDH), and the cat was referred for further investigations and surgical treatment. Computed tomography (CT) of the thorax confirmed the presence of a large PPDH and individuated the existence of a heterogeneous mass lesion in the caudal mediastinum. Additionally, there were disseminated lesions affecting multiple organs, numerous skeletal muscles, and several lymph nodes. On the basis of these findings and a likely neoplastic cause, the owner elected to have the cat euthanised. Postmortem examination and histopathological analysis revealed the presence of a pulmonary adenocarcinoma, invading and compressing the distal part of the oesophagus and a large bronchus, and likely representing the cause of the patient's main clinical signs.