A 20-year single-institution experience of clinical stage I nonseminomatous germ cell tumors of the testis (NSGCTT) in childhood and adolescents was reviewed in relation to clinical characteristics, treatment modalities, and survival. Thirty-one patients with clinical stage I NSGCTT were seen between 1980 and 2000: 14 children and 17 adolescents. Yolk sac tumors and/or teratomas occurred in the children, whereas mixed histologies, including embryonal carcinoma, were predominant in the adolescents. After orchiectomy, the children were assigned to surveillance and the adolescents to active treatment: 16 underwent retroperitoneal lymph node dissection (RPLND) and 1 had adjuvant cisplatin-based chemotherapy because of a high-risk histology. Three of the 14 children (21.4%) relapsed 3, 7, and 8 months after orchiectomy: all 3 had yolk sac tumors and presented with increased alpha-fetoprotein levels. No patients had retroperitoneal relapse; two recurred locally and one in the lung. All three children were treated with cisplatin-based chemotherapy with or without surgery. Among the 16 adolescents undergoing RPLND, 4 (25%) had nodal metastases. Three of the 12 patients (25%) who had negative nodes at RPLND relapsed in the lung 3, 7, and 8 months after RPLND. All were treated with cisplatin-based chemotherapy with or without surgery. Five-year relapse-free and overall survival rates for the whole series were 80.6% and 100%, respectively. This series enabled the authors to pinpoint several important aspects of stage I NSGCTT in children and adolescents. In particular, almost all the childhood cases had the same yolk sac tumor histology, the children tended to have localized disease, and an increased alpha-fetoprotein level had a very high predictive value, suggesting that follow-up should include AFP measurements. A conservative approach is the best option in children, while adolescent NSGCTT behaves like the adult disease and management must include similar treatment strategies.