A 7-year-old female neutered British Short Hair cat was presented for further investigation and treatment of pleural effusion due to a possible pyothorax. Cytology and culture of the fluid identified pyothorax and a large mass/consolidated right caudal lung lobe was found on x-ray, ultrasound and CT scan. Lung lobectomy was performed and a diagnosis of pulmonary lymphomatoid granulomatosis (PLG) was confirmed by histopathology and immunohistochemistry. Despite medical treatment the patient was euthanized due to progression of the disease and deterioration of her clinical signs. This is the second case of PLG reported in a cat and the first case of PLG with concurrent pyothorax. PLG, despite being very rare, should be added to the list of differential diagnoses for pyothorax and solitary lung masses in cats.