CD10 is a cell surface-related neutral endopeptidase that is involved in cleaving cytokine peptides; it may also play a role in the proliferation of tumor cells and their acquisition of invasiveness. On account of its association with other overtly epithelial neoplasms, we hypothesized that CD10 might be preferentially expressed in the sarcoma-like components of sarcomatoid carcinomas as compared with true sarcomas. Immunohistochemical labeling for CD10 was assessed in various sarcomas and sarcomatoid carcinomas. An aggregate score was generated using both the intensity and extent of staining throughout the neoplasms. Overall, CD10 was expressed more often in true sarcomas (27 of 33 cases) as contrasted with sarcomatoid carcinomas (22 of 34 cases), but with no statistically significant difference between the 2 groups. Uterine "carcinosarcomas" expressed CD10 with accentuation in periglandular tumor cells. The sarcoma-like components in squamous cell carcinoma of the respiratory tract (larynx and lung), tongue, bladder, skin, and penis also expressed CD10 consistently. In the final analysis, there was no difference in CD10 expression between sarcomatoid carcinomas and true sarcomas. This marker seems to have little, if any, differential diagnostic value in the specified histopathologic context.