Diabetes mellitus produces serious complications in several major organ systems. The pulmonary complications, although uncommon and not well recognized, may be life-threatening. We describe a 20-year-old patient with diabetic ketoacidosis in whom pulmonary zygomycosis developed. This condition was complicated by stenosis of the left upper lobe bronchus despite successful treatment of the zygomycosis. Bronchial obstruction has become a well-recognized complication of pulmonary zygomycosis. In addition to infections caused by Zygomycetes, mycobacteria, viruses, and bacteria, the pulmonary complications described in patients with diabetes include pulmonary edema, disordered breathing during sleep, and reductions in elastic recoil of the lungs, diffusing capacity of the lungs for carbon monoxide, and bronchomotor tone. Other reported complications are respiratory alkalosis, cardiorespiratory arrest, pneumothorax, pneumomediastinum, plugging of the airways with mucus, and aspiration pneumonia attributable to diabetic gastroparesis.