We report here the youngest known IgM myeloma patient to have presented wit
h a mandibular mass. A 22-year-old Chinese man sought medical attention due
to a mass over his right mandible that had been growing progressively for
6 months. A solitary osteolytic lesion in the right mandible was identified
radiologically. Incisional biopsy revealed the presence of plasma cells of
monoclonal origin, as evidenced by the exclusively positive staining of th
e kappa light chain. The diagnosis of multiple myeloma with mandibular invo
lvement was confirmed by bone marrow examination. Further tests, including
immunoglobulin electrophoresis and assay of the serum levels of kappa and l
ambda light chains, demonstrated that his myeloma was of the IgM, kappa sub
type, The patient achieved a nonsustained partial response to six courses o
f melphalan and prednisolone therapy and palliative radiotherapy.