A case of I-cell disease is reported. The patient suffered from several episodes of pneumonia, and died of pneumonia at 12 months of age. Tissue specimens obtained at autopsy were stained with colloidal iron to demonstrate acid mucopolysaccharides. Characteristic foamy changes were observed in organs such as the heart, kidneys, liver, spleen and brain. An interesting finding in this case was that not only the interstitial cells but the alveolar epithelium in the lung showed the same foamy changes. The major causes of death of patients with I-cell disease are congestive heart failure and recurrent respiratory infections. However, there have been few reports on the histological changes in the lungs, and none have described the changes in the alveolar epithelium. Further cases must be investigated to examine the pathological relation between the histological changes in the lungs and the cause of death, because recurrent respiratory infections are the major contributor to death in patients with I-cell disease.