Five cases of von Recklinghausen's neurofibromatosis were examined electron‐microscopically. The tumors were composed of Schwann cells, myelinated and non‐myelinated axons, fibroblasts, collagenous fibers, endothelial cells and mast cells. From our observation, the Schwann cells as well as the fibroblasts were capable of producing collagenous fibers. This observation was strengthened by the following findings: (a) collagenous fibers were just adjacent to Schwann cell surface, occasionally showing a banded structure; (b) the vesicular elements similar to those of the fibroblasts were observed within the cytoplasm of Schwann cells. Each Schwann cell was invariably surrounded by a basement membrane, and in the area of the collagenous fibers formed, the basement membrane became a hazy homogeneous substance extending irregularly into the connective tissue space. The membrane bounded vesicular elements appeared to discharge their content into the extracellular space after fusion with the cell membrane, and here the basement membrane as well as the cell membrane became obscure and looked homogenous. The tumors of von Recklinghausen's neurofibromatosis were basically composed of both Schwann cells and fibroblasts. The name “neurofibroma” seemed suitable for these types of