Besides its role in cell adhesion, beta-catenin exerts a function as an oncoprotein. The aim of this study was the characterization of its expression, possible mutation, and the assessment of beta-catenin as a prognostic indicator for soft tissue sarcomas. A total of 115 soft tissue sarcomas were analyzed using immunohistochemistry, immunogold-electron microscopy, and DNA analysis. Information from 56 patients was available for follow-up. A statistically significant correlation was found between intracellular distribution of beta-catenin and the proliferative activity (MIB-1 expression) in high-grade sarcomas (P = .0008). Beta-catenin was identified with intracytoplasmic and nuclear accumulation, showing additional membranous staining in sarcomas with epithelioid pattern. Ultrastructurally, a colocalization between beta-catenin and nuclear heterochromatin was demonstrated. In 22 analyzed tumors, only one (yet undescribed) mutation of the beta-catenin gene (C-A transversion) could be detected. Prognostic validity of the cellular expression of beta-catenin, however, was not proven. Apart from its membranous function as an effective molecule for cell-adhesion in sarcomas with epithelioid pattern, beta-catenin may act as an oncoprotein in sarcomas with intracytoplasmic and nuclear localization with binding to nuclear DNA. A previously discussed stimulation of cell proliferation caused by an increased beta-catenin level can also be postulated for high-grade soft tissue sarcomas in correlation with the rate of proliferation. Mutations of the beta-catenin gene are probably of lesser importance for the accumulation of beta-catenin in soft tissue sarcomas.