Bone marrow involvement was found in 21 of 56 patients with undifferentiated carcinoma of the nasopharyngeal type UCNT whose nasopharyngeal and bone marrow biopsies were available. Radiotherapy and chemotherapy (cisplatin, 5-fluorouracil and bleomycin) were given because of distant metastases. The microscopic aspects of bone invasion were investigated and were classified into three subtypes osteolytic, osteosclerotic and mixed type. The UCNT patients population was 10 years younger than that studied previously. Both the extent of the primary tumor (T) and cervical lymph node status (N) exerted an influence on the probability of metastases developing. Chemotherapy given to patients must be improved because UCNT with bone metastases is a disease with a poor prognosis.