A 3-month-old infant with congenital hypotonia suffering from an unusual form of glycogenosis is reported. The most striking neuropathologic findings were vacuolation of neuropile and glycogen accumulation, especially in the cerebral cortex and cerebellar molecular layer. Ultrastructurally, glycogen accumulation was present mainly in neurites and astrocytic processes, and mostly appeared as rosettes (alpha glycogen particles). Biochemical analysis of glycogen in various regions of the central nervous system showed an increase of up to 100-fold. The cerebral cortex, deep nuclei, and cerebellar cortex had the highest glycogen elevations, while the cerebral white matter glycogen level was normal. Among other tissues, the heart showed a several-fold increase in glycogen content. Muscle, liver, and kidney glycogen levels were not elevated. Findings in this case and in three other reported patients with cerebral glycogenosis of alpha particle type are discussed.