We have evaluated epidemiology, prognosis and the association between metastases and local recurrence in a series of adult patients with soft tissue sarcoma (STS) of the extremity and trunk wall. 508 patients were diagnosed in the Southern Swedish Health Care Region from 1964 through 1989. The series was population-based, i.e., all patients within a defined area were included, irrespective of where treated, thereby avoiding selection bias in referral and follow-up. Epidemiology. The annual incidence was 18 per million. The median age was 64 years. One third of the tumors were subcutaneous, and these were smaller than the deep-seated tumors. Malignant fibrous histiocytoma and grade IV were the commonest. Differences were noted in clinicopathologic features among histotypes. The 5-year metastasis-free survival rate (MFSR) was 0.6. The crude local recurrence rate was 0.3. The majority of metastases and local recurrences occurred within 3 years. The referral pattern to the tumor center has become more favorable over time; in the last 5 years half of the subcutaneous and four fifths of the deep-seated tumors were referred before surgery. Prognostic factors. Tumor size, tumor necrosis, and vascular invasion were strong and independent prognostic factors for metastasis in a histologically mixed series. In MFH, storiform and pleomorphic subtype, tumor necrosis and tumor size were associated with a poor prognosis. Tumor necrosis and vascular invasion independently worsened the prognosis in leiomyosarcoma. In liposarcoma, tumor necrosis and in synovial sarcoma, tumor size were the only important prognostic factors. Tumor size, tumor necrosis, and vascular invasion were used in a prognostic system which identified two thirds of all patients with a 5-year MFSR of 0.8 and one third of the patients with a 5-year MFSR of 0.3. Metastasis and local recurrence. The causal association proposed for local recurrence and metastasis should be interpreted with caution. We suggest that highly malignant tumors combine local and distant aggressiveness, and that local recurrence is a marker of risk, and not necessarily a cause of, metastasis. Conclusions. 1. Population-based series are preferable when studying epidemiology in soft tissue sarcoma. 2. We propose that tumor size, tumor necrosis, and vascular invasion are strong and reliable factors that can be used to improve prognostic accuracy. 3. There is a growing body of evidence against a causal relationship between local recurrence and metastasis.