Autopsy samples were obtained from a 12.5-year-old girl who died with a neurologic disorder consisting of myoclonus, myoclonic epilepsy, spasticity, strabismus, and mild mental retardation but no hepatosplenomegaly. Studies in leukocytes, cultured skin fibroblasts, brain, liver, and spleen of this patient revealed glucosylceramide β-glucosidase (EC 3.2.1.45, glucocerebrosidase) activity about 10% of controls, and well in the range found in samples from Gaucher disease patients. Extraction of the lipids from liver and spleen with chloroform-methanol (2:1) did not show accumulation of glucosylceramide or other lipid. Examination of the lipids in brain by high performance liquid chomatography revealed the presence of glucosylceramide, which is not found in brain samples from controls. Pathologic examination of the liver and spleen revealed no evidence of Gaucher disease. The brain showed many degenerative lesions and loss of neurons. There was no complementation of glucocerebrosidase activity when the cells from this patient were hybridized with cells from patients with Type 1 or Type 2 Gaucher disease. The reason for the lack of glucosylceramide storage in the liver and spleen has not been determined.