1. Twenty-five cases of benign giant-cell tumour of bone, treated at Westminster Hospital, London, are reported.

2. The diagnosis can often be made on clinical and radiographic grounds alone but biopsy is sometimes necessary and seldom, if ever, contra-indicated.

3. Some cases may best be treated by excision, but in general irradiation is the treatment of choice.

4. Details of treatment by irradiation are given.

1. Fifteen new cases of plasma cell tumour are reported with a review of the literature.

2. Case examples are quoted to show the gradual merging of the different clinical and pathological syndromes into one entity.

3. A comprehensive analysis of the various manifestations of the disease is made.

4. An attempt is made to correlate the widely differing features of the disease-process and a classification is given.

5. It is considered that metastasis plays no part in this condition.

6. The variety of forms of plasma cell tumours are shown as gradations of an essentially similar disease-process, and are not regarded as separate conditions.