We examined bcl-2 expression as well as p53 expression and mutation in human uterine smooth muscle tumours to determine the influence of bcl-2 expression on prognosis in patients with uterine leiomyosarcomas. bcl-2 protein was expressed in nearly all benign smooth muscle tumours but in only 57% of leiomyosarcomas. Benign smooth muscle tumours were usually negative for p53 protein, but 16 out of 21 (76%) leiomyosarcomas were positive. A p53 gene mutation was detected in nine of the 16 leiomyosarcomas that showed p53-positive staining. A significant positive correlation was observed between p53 mutation and p53 expression, between the number of mitoses and the Ki-67 labelling index, and between clinical stage and p53 mutation. A significant negative correlation was observed between bcl-2 expression and p53 mutation, and between bcl-2 expression and p53 overexpression. Univariate survival analysis revealed that bcl-2 expression, p53 mutation and clinical stage (stage 1 vs stages 2-4) all showed a significant correlation with prognosis. In a multivariate stepwise regression analysis, positive bcl-2 expression and stage 1 disease were the independent predictors of a favourable prognosis. Our results suggest that bcl-2 is frequently expressed in human uterine smooth muscle tumours, and that its expression may correlate with a favourable prognosis in patients with uterine leiomyosarcoma.