Nephroblastoma-like tumors (NLTs) developed in metastatic sites in nine men with testicular germ cell tumors (GCTs). These tumors had a characteristic "triphasic" admixture of primitive tubular structures, sometimes with a glomeruloid pattern, blastema and stroma. Skeletal muscle differentiation was apparent in two cases. Specific neuroendocrine markers (synaptophysin and chromogranin A) were negative. All patients were treated by surgical excision. Six patients were alive with no evidence of disease from 4 to 12 years after diagnosis of GCT and NLT. One patient was alive with disease 6 years after diagnosis of GCT and 3 years after diagnosis of NLT. One man who also had metastatic primitive neuroectodermal tumor (PNET) had short survival, and one patient died of postoperative infection. We conclude that patients with testicular GCTs in whom NLTs develop in metastatic sites often experience prolonged survival. Surgical excision appears to be adequate treatment for NLT arising in metastatic testicular GCT in most patients. It is important to distinguish NLTs from PNETs in metastatic GCTs because of the more aggressive course and the frequently fatal outcome of the latter.