The spinal nerve roots were studied in two siblings with Werdnig-Hoffmann disease (WHD). An invasion by fibrous astrocytes was consistently seen along the atrophic ventral roots, more extensively in the older sibling. The parallel glial processes extended in discrete bundles and were always enclosed by a basal lamina. Loss of unmyelinated axons and probable glial extension along unmyelinated fibers were also seen. The astrocytic processes with abundant microtubules and prominent junctional devices resembled those of the subpial region, which appeared to have gained access into the ventral roots following axonal degeneration. The present observations suggest that such glial migration, although apparently unique in WHD, is a secondary phenomenon and fails to resolve the issue as to whether neuronal degeneration or an injury to the nerve roots is the primary event in this disorder.