A 6 1/2 month old male infant presented a week after his birth with secretory diarrhea of unknown etiology. He was sustained by central hyperalimentation for the rest of his life, and treated for presumed sepsis with a wide variety of antibiotics. The brain showed vacuolation in the diencephalic nuclei and white matter of the brain stem. There were also many clusters of enlarged Purkinje cell dendrites in the molecular layer. In Golgi preparations the primary and secondary dendrites showed segmental swellings and absent tertiary branchlets. The swellings were due to remarkable accumulations of mitochondria. The pathogenesis of the dendritic changes is discussed, and 'dying back' phenomenon is proposed to explain the changes.