Carcinosarcoma is an aggressive neoplasm of the female genital tract, which comprises 1-2% of malignancies of the uterine corpus. Because of the broad range of differentiation exhibited by these tumors, the precise nature of the relationship between epithelial and stromal components in this unique tumor remain unclear. Previous studies have demonstrated that mutation and consequent overexpression of the tumor suppressor gene p53 occurs frequently in carcinosarcoma and is conserved from primary to metastastic sites. We examined p53 accumulation in formalin-fixed, paraffin-embedded archival sections in 19 cases previously shown to have mutations in the p53 gene and performed semi-quantitative analysis of the intensity of staining and relative density of positive cells and stromal and glandular elements. There was a high level of concordance of immunohistochemical staining for the p53 oncoprotein between glandular and stromal elements. These results further suggest a clonal origin for the diverse elements of carcinosarcoma.