GM1-gangliosidosis is a disease characterized by abnormal accumulation of GM1-ganglioside in the brain and viscera. The disease is characterized by clinical findings similar to Hurler's disease and pathologic features resembling Niemann-Pick's disease but with involvement of the glomerular epithelium. A 14-month-old boy, clinically diagnosed as GM1-gangliosidosis, died of respiratory insufficiency and was autopsied except for the brain. Biochemically, marked increase of GM1-ganglioside in the viscera was demonstrated. Pathologically, the foam cells were present in the viscera. Some parts of the cytoplasmic vacuoles in the lungs and spleen contained osmiophilic fibrillar material electron-microscopically. This case was characterized by marked accumulation of foam cells in the pulmonary alveolar spaces.