A 25-year-old male patient with a biphasic synovial sarcoma of his right flank is reported. The tumor was not only richly glandular but also showed a rare finding in association with a sarcoma, namely, squamous differentiation. Light microscopy and electron microscopy demonstrated the classical features of a biphasic synovial sarcoma except for foci of squamous change. Antibody stain directed against keratin demonstrated this substance in both the glandular and squamous cells but not in the stromal elements. Therefore, the finding of squamous differentiation in association with a malignant, deep soft-tissue tumor must include in the differential diagnosis not only carcinomas but rare sarcomas as well, including the biphasic synovial sarcoma and the glandulosquamous variant of malignant schwanomma.