GM1 gangliosidosis (type 1) is a rare hereditary, autosomal recessive, lysosomal storage disease characterized by a marked deficiency of active acid beta-galactosidase resulting in accumulation of gangliosides and mucopolysaccharides in tissues. Disease status of newborns from affected kindreds may be diagnosed by placental examination. Typical findings include a characteristic vacuolar distension of the cytoplasm of syncytiotrophoblast and stromal Hofbauer cells. We report a case of unsuspected fetal storage disorder initially diagnosed by routine placental examination of a normal-appearing infant born to a previously unaffected family. Progressive, third-trimester oligohydramnios and fetal growth retardation had been documented by ultrasonography. Placental findings included vacuolization of syncytiotrophoblast, intermediate trophoblast, and stromal Hofbauer cells. Subsequent enzyme analysis confirmed the placental findings of storage disorder and diagnosed GM1 gangliosidosis.