Among the many lesions removed surgically from synovial-lined structures and registered With the Army Institute of Pathology during the years of the second World War were thirty-two examples of the malignant neoplasm usually designated as synovioma.

Certain cytological and structural features distinguish this type of neoplasm from other mesenchymal tumors. These cell patterns may be explained by referring to the anatomical and physiological Peculiarities of the normally developing and mature synovial tissues.

Although the determination of the fatality rate in the present series must await the completion of the follow-up study which is now in progress, the knowledge that sixteen patients have died, have had metastases, or have shown local recurrences, points again to the seriousness of this neoplasm, as well as to the necessity for its Prompt and complete surgical removal.

The present observations indicate a need for a follow-up study of the many cases in which synovial-membrane lesions, now regarded as benign, have been removed. Such an investigation should aid in determining the future course of these lesions of varied histological patterns and there by serve as a guide for appropriate treatment.