BACKGROUND: Early experiments using ligand-binding assays demonstrated the presence of estrogen receptor (ER) in fibromatoses. These findings were not confirmed by later studies using immunohistochemical analysis. METHODS: To verify the expression of ERs in fibromatosis as well as to clarify the inconsistency between radioligand and early immunohistochemical studies, the authors examined a series of 40 extraabdominal fibromatoses using antibodies raised against ERbeta. RESULTS: All 40 cases of extraabdominal fibromatosis were at least focally positive for ERbeta. Thirty-three of 40 (83%) displayed 3+ (>50%) expression, 5 of 40 (12%) were 2+ (11-50%), and 2 of 40 (5%) cases showed 1+ (<10%) expression. All cases were negative for ERalpha. CONCLUSIONS: Although extraabdominal fibromatosis does not express ERalpha, there appears to be nearly uniform expression of ERbeta. This finding clarifies discrepancies in the literature regarding estrogen expression in fibromatosis, and provides a biological mechanism for the action of antiestrogenic compounds in the treatment of fibromatosis. Estrogen antagonists may have a role in the treatment of refractory or recurrent extraabdominal fibromatoses.