The nuclear DNA content of 148 high-grade soft tissue sarcomas of the extremities and trunk was determined by flow cytometry, using tumor material from paraffin-embedded tissue. The patients were part of a prospective randomized clinical trial on the efficacy of adjuvant single-agent chemotherapy with doxorubicin. Chemotherapy did not improve the metastasis-free survival (MFS). After a median follow-up time of 48 months (range, 2 to 97), a multivariate analysis of prognostic factors for developing metastatic disease was performed. DNA aneuploidy was found to be an independent prognostic risk factor in addition to histologic malignancy grade IV, intratumoral vascular invasion, tumor size over 10 cm, and male sex. Patients with none or one risk factor had a 5-year MFS of 79%, with two risk factors 65%, with three risk factors 43%, and with four and five risk factors 0%. About one half (78 of 148) of the patients with three factors or less belonged to a group with a MFS over 60%. The combination of different risk factors, including DNA aneuploidy, seems to be a useful prognostic model for soft tissue sarcomas, which could be of value to select high-risk patients for further trials with adjunctive therapy.