Grading based on histopathologic features is used to predict survival in soft-tissue sarcoma. However, variations in clinical behavior between tumors of the same grade motivate a search for additional factors that correlate with prognosis. Proliferating cell nuclear antigen (PCNA) is expressed in proliferating cells during the G1, S and G2-phases. To evaluate a prognostic implication of PCNA, the tumors of 48 patients with malignant fibrous histiocytomas (13 grade III, 35 grade IV) with a minimum follow-up of 2 years were immunohistochemically studied. We used PC10, a monoclonal antibody (MAb) directed against PCNA, which allows cell proliferation in formalin-fixed, paraffin-embedded tumor tissue to be evaluated. We applied a semiquantitative PCNA grading scheme to all stained nuclei of an entire slide. The 3-year metastasis-free survival rate was 0.87 for patients in grade A (low PLNA rate), and 0.14 for patients in grade C (high PLNA). Our findings show that immunohistochemical evaluation of cell kinetics in soft-tissue sarcomas by PCNA might be a useful adjunct to conventional tumor grading.