The p21 protein inhibits cyclin-dependent kinases and mediates cell-cycle arrest and cell differentiation. It is induced by wild-type p53, but not by mutant p53. This study of 75 patients with endometrial carcinoma investigates the relationship between p21 expression and the functional status of p53, and the usefulness of p21 as a prognostic marker. Correlations were determined between p21 immunoreactivity, p53 overexpression as examined by immunohistochemistry, p53 DNA mutations as examined by polymerase chain reaction-single-stranded conformation polymorphism (PCR-SSCP) analysis, and clinicopathological features, including the clinical outcome. Immunoreactivity for p21 and p53 mutations were detected in 47 (62.7 per cent), 37 (49 per cent), and 23 (31 per cent) patients, respectively. There were no significant correlations between the presence or absence of p21 immunoreactivity and p53 overexpression and DNA mutations. Survival curves revealed that patients with p53 overexpression tended to have a poorer prognosis than those without p53 overexpression (P = 0.104), that patients with p53 mutations had a significantly worse prognosis than those without mutations (P = 0.035), and that patients with p21 expression tended to have a better prognosis than those without p21 expression (P = 0.074). Immunohistochemical analysis of p21 was not useful for evaluating the functional status of p53 in patients with endometrial carcinoma. Both p21 expression and p53 abnormalities were considered as prognostic indicators in patients with endometrioid endometrial carcinoma.