Abstract
Malignant mesenchymoma within the right ulnar nerve of an 8 year old boy is described. The patient did not have stigmata of von Recklinghausen's neurofibromatosis. The growing and painful tumour was excised five and a half detection, and recurred five months later. Mingling of the nerve sheath sarcoma and rhabdomyosarcoma was noted within the same mass which was separated from the adjacent striated muscles. It is suggested that this mesenchymoma arose from mesenchymal cells or cells of mesenchymal type comprising the peripheral nerve sheath which is derived from ectomesenchyme of the neural crest.