Since the long-term disease-free survival rate in adjuvantly treated osteosarcoma has nowadays reached a level of about 70%, increasing interest is also being directed towards primarily disseminated forms of the disease. Primary metastases, which were confined to the lungs in 42 cases, were detected in 59 out of 421 patients from the prospective therapy trials COSS-80 and COSS-82. The primary tumors were more frequently localized in the proximal femur and flat bones as compared to patients without detectable metastases at diagnosis. Following chemotherapy and surgery of the primary tumor, 15/31 (48%) patients whose metastases were excised have survived for 4-8 years, in contrast to only 1/22 (5%) of those patients whose metastases could not be removed for a variety of reasons. Clinical or histological evidence of tumor response after primary chemotherapy significantly influenced the outcome of the metastasectomized patients.