Our study was performed to clarify whether the combination of DNA flow-cytometric and quantitative histopathological parameters improves the prediction of occult metastatic disease in clinical stage-I non-seminomatous testicular germ-cell tumors (NSGCT). We used archival paraffin primary-tumor tissue of 67 clinical stage-I NSGCT patients who had undergone retroperitoneal lymph-node dissection (RPLND). According to the RPLND specimens, 24 patients were at pathological stage I and 43 at pathological stage II. Archival blocks were redissected for histological re-evaluation. In addition, 50 μm sections were prepared according to the Hedley technique in order to obtain nuclear suspensions which were processed for flow cytometry (FC). In univariate analysis, the percentage of embryonal carcinoma, the percentage of immature teratoma and vascular invasion were the most accurate predictive histopathological parameters. The percentage of aneuploid cells in S-phase was the best predictive FC parameter. In multivariate analysis, the percentage of embryonal carcinoma and the S-phase fraction of aneuploid cells were the only independent markers for occult metastatic disease. According to this statistical approach, 91.0% of pathological stage-I and stage-II cases were correctly classified. Sensitivity was 95.3% and specificity was 83.3%. Using histopathological criteria alone, only 56.7% NSGCT patients were correctly classified.