A 16-year-old, neutered male, domestic shorthaired cat was presented with a history of progressive lethargy and decreased appetite. Serum biochemical profile demonstrated hypercalcemia, and thoracic radiographs and computed tomography were consistent with pulmonary neoplasia. A thoracotomy was performed, and a pulmonary mass was removed. Histopathology diagnosed a bronchogenic adenocarcinoma, and calcium levels returned to normal limits after excision of the mass. While bronchogenic adenocarcinoma has been a suspected cause for hypercalcemia in cats, to the authors' knowledge, this is the first proven account.