Between 1981 and 1986, 279 consecutive patients with clinical stage I (CS1) nonseminomatous germ cell tumors (NSGCT) of the testis underwent pathological staging (PS) with retroperitoneal lymphadenectomy (RPLND). Patients with retroperitoneal metastases (PS2) received adjuvant chemotherapy. The median follow-up time after RPLND was 50 months (range, 30 to 90). Clinical and histopathologic features were registered prospectively and analyzed for association with risk of having PS2, relapse despite pathological stage 1 (PS1) or the combined risk of either event, metastatic disease (MET). Seventy-five (26.9%) of the patients had PS2 disease, and 30 (14.7%) of the 204 PS1 patients relapsed, indicating that at least 105 (37.6%) of this CS1 population had subclinical MET at the time of orchiectomy. Four (1.4%) of the 279 CS1 patients died of testicular cancer. Multivariate analyses showed several variables to be significantly associated with outcome for the CS1 patients; vascular invasion in primary tumor and normal preorchiectomy serum alpha-fetoprotein (Pre-AFP) level indicated PS2 disease. If Pre-AFP was excluded from the model, the absence of teratoma or yolk sac elements in the primary tumor became significant predictors of PS2. Vascular invasion, absence of teratoma, and a short interval between orchiectomy and RPLND indicated increased risk of relapse in PS1 patients. Vascular invasion, normal Pre-AFP, absence of teratoma elements, and a short orchiectomy to RPLND interval were predictive of MET. Our results indicate that prognostic factors useful for stratification of CS1 patients with NSGCT to different treatment options may be established.