We describe a case of desmoplastic infantile ganglioglioma (DIG) arising in the ventral diencephalon of a 3-1/2-month-old boy. On biopsy, the tumor featured a desmoplastic, S-100 protein and GFAP immunoreactive stromal element, as well as a variable spectrum of ganglion cells. Electron microscopy demonstrated astrocytes, and morphologically fibroblasts, as well as neurons containing 120-nm dense core granules. In addition, tubular structures composed of tightly apposed cells with features of astrocytes and of Schwann-like cells were also noted. Devoid of fibroblasts, the tubular structures were surrounded by a single basal lamina. At autopsy 6 years later, the multinodular, cystic mass had replaced the diencephalon, extended into both temporal lobes as well as the optic nerves, and showed marked leptomeningeal involvement. Microscopically, superficial portions of the tumor consisted of typical DIG, whereas deep, nondesmoplastic portions exhibited pattern variation ranging from pilocytic astrocytoma to ganglioglioma and gangliocytoma. There was also a minor element of small, 'primitive-appearing' neuroepithelial cells. Dysplastic ganglion cells variously reactive for neurofilament protein and synaptophysin were present throughout the tumor. Our study not only confirms DIG as a variant of ganglioglioma, one capable of slow growth, infiltration, and fatal progression but suggests that its differentiating potential includes elements of both the central and peripheral nervous systems. If so, their derivation may be from multipotential cells of the neural plate.