Mutation and overexpression of p53 have been described in uterine malignant mixed Müllerian tumours and in endometrial adenocarcinoma, where it has been associated with a poor prognosis. This study examines p53 expression and mutation of the p53 gene in benign and malignant smooth muscle tumours of the uterine corpus. p53 expression was evaluated by immunohistochemistry in formalin-fixed, paraffin-embedded tissue from 23 leiomyosarcomas, 10 tumours of uncertain malignant potential (TUMPs), and 18 leiomyomas. Single-stranded conformational polymorphism, (SSCP) analysis of exons 5-8 of the p53 gene was performed on 13 leiomyosarcomas, nine TUMPs, and eight leiomyomas. With microwave antigen retrieval, p53 immunoreactivity was seen in 13/23 microwave treatment, staining was abolished in three leiomyosarcomas, all immunoreactive TUMPs, and the single positive leiomyoma. SSCP analysis revealed mutation in three leiomyosarcomas. There was one mutation in exon 5 in a case with positive immunohistochemistry. Two cases with negative staining showed mutation, one in exon 7 and one in exon 8. Mutation was present in exon 7 in 4/9 and in exon 6 in 1/9 TUMPs. All of these cases showed positive immunohistochemistry. There was no significant difference in outcome between cases with and without positive immunohistochemistry. p53 expression is seen in a significant proportion of uterine leiomyosarcomas. Microwave antigen retrieval increases the proportion of positive cases and also results in positive staining in TUMPs. Mutation of the p53 gene occurs in only a minority of leiomyosarcomas and in a significant proportion of TUMPs. Positive immunohistochemistry does not, however, correlate with the presence of mutation and other factors may be responsible for p53 detection in many cases.