Objective. To evaluate the clinical significance of DNA ploidy pattern for patients with nonseminomatous germ cell testicular tumors who did not receive platinum-based chemotherapy. Methods. Flow cytometric nuclear DNA ploidy analysis of paraffin-embedded tissue blocks were used. Results. All patients underwent radical orchiectomy with or without retroperitoneal lymphadenectomy between 1960 and 1980. Mean follow-up time was eight years. Nineteen percent of the tumors were DNA diploid and 81 percent were DNA aneuploid. Signs of local tumor extension (spermatic cord involvement or vascular invasion) were found in 20 tumors, all were classified as DNA aneuploid (P < 0.04). After primary treatment 9 patients who were clinically cured experienced disease progression; only 1 of them had DNA diploid tumor; the rest were DNA aneuploid (P < 0.05). The ten-year survival rate was higher for patients having DNA diploid tumors compared with those with DNA aneuploid neoplasms (86% versus 53 percent, P < 0.02). Conclusions. The results of this retrospective study indicate that nuclear DNA content provide important information concerning the natural history and biology of nonseminomatous germ cell testicular tumor.