A 13.5 year old spayed female DSH presented with the chief complaints of dyspnea, anorexia, and weight loss. The cat lived strictly indoors and had previously tested negative for both FeLV and FIV. In addition to the anorexia, weight loss, and dypsnea, the patient was dehydrated and extremely tachypneic. Mild wheezes and increased brochovesicular lung sounds were auscultated bilaterally. Previous visits to the referring veterinarian and a cardiologist had revealed a diffuse bronchoinstitial lung pattern on radiographs, a normal echocardiogram, negative fungal cultures, and a non-diagnostic lung aspirate. No improvement in clinical signs or on radiographs was observed after treatment with broad-spectrum antibiotics, prednisone, and aminophylline. Bloodwork at Cornell was unremarkable, and she tested negative for FIP, Aelurostrongylus abstrusus, and toxoplasmosis. A diagnosis of spontaneous feline idiopathic pulmonary fibrosis (IPF) was made based upon characteristic histopathological lesions from a lung biopsy. Spontaneous feline IPF is a rare and newly described disorder that shares similarities with a syndrome well characterized in human beings. Hallmarks include interstitial fibrosis, alveolar epithelial metaplasia, type II pneumocyte hyperplasia, and alveolar interstitial smooth muscle hypertrophy. Interstitial inflammation is reportedly mild. A mutation in the surfactant protein C gene has been proposed to cause abnormal cytoplasmic lamellar body-like inclusions in type II pneumocytes. No effective treatment has proven to prolong survival in humans.