In recent years less intensive chemotherapy programs for patients with metastatic nonseminomatous germ cell tumors with high likelihood of cure have been proposed, and the use of innovative more intensive treatments for patients with less favorable prognosis is being explored. The development of validated prognostic classifications has thus become important. In 77 patients with metastatic nonseminomatous germ cell tumors treated with chemotherapy, the ability of various prognostic factors to predict outcome of treatment was assessed. The multifactorial prognostic classification (Indiana classification) and a mathematical predictive formula correctly allocated patients to low- or high-risk groups in 84.4 percent and 87.0 percent of cases. The multifactorial classification system (M.D. Anderson system) correctly allocated patients in 61 percent of cases. The presence of serum beta HCG levels over 1,000 mg/mL, a pure choriocarcinoma histology and possibly an extragonadal primary origin of tumor were found to predict an adverse outcome in a small number of patients. It is concluded that use of the Indiana classification or mathematical predictive formula is an accurate means of allocating patients with metastatic germ cell tumors to high- or low-risk groups and that allocation of patients with pure choriocarcinoma histology, very high beta HCG levels, or extragonadal primary origin of tumor to the poor prognosis category will improve the accuracy of prediction in a few cases.