A consecutive series of 100 patients operated on for lesions that were assumed to be soft tissue tumors, all of whom had been the subject of fine-needle aspiration in the preoperative investigation, is described. A correlative study of smears and the light- and electron-microscopic findings of embedded fine-needle aspirates and the histopathology of the surgical specimens was performed. Eighty of the lesions were found to be genuine soft tissue tumors, of which 51 were sarcomas. The other 20 cases were either metastatic carcinoma, malignant melanoma, or malignant lymphoma. The embedding technique produced additional light-microscopic information about tissue structure and growth pattern, and electron-microscopic information about tissue and cell differentiation of importance to the diagnosis. In the case of certain types of soft tissue tumor, such as lipoma, neurilemmoma, liposarcoma, and malignant fibrous histiocytoma, and for well-differentiated metastatic carcinoma and pigmented malignant melanoma, the diagnosis may be strongly suggested by the appearance of the smears; the embedding technique serves to further support the diagnosis. In the case of small round-cell malignancies, the ultrastructural examination proved to be of special value, ie, in the distinction of rhabdomyosarcoma, poorly differentiated metastatic small cell carcinoma and malignant melanoma, and occasional cases of malignant lymphoma. Spindle cell sarcomas, such as leiomyosarcoma when well differentiated, biphasic synovial sarcoma when it includes glandular structures, and malignant hemangiopericytoma, could be recognized ultrastructurally, although electron-microscopy generally failed to reach a definite diagnosis as to the subtype in most cases of poorly differentiated spindle-cell sarcoma.