Background: Patients with clinical stage I (CS I: cN0M0) germ cell tumors (GCT) exhibit favorable oncologic outcomes. While prognostic features can help inform treatment in adults with CS I GCT, we lack reliable means to predict relapse among pediatric patients. We sought to identify predictors of relapse in children with CS I GCT. Methods: We performed a pooled post hoc analysis on pediatric CS I GCT patients enrolled in 3 prospective trials: INT-0097 (phase II), INT-0106 (phase III), and AGCT0132 (phase III). Pathology was centrally reviewed. Patient demographics, pT stage, serum tumor markers, margin status, histology, relapse, and survival were compiled. Cox regression analyses were used to identify predictors of outcomes. Results: 88 patients were identified with histologic data available. Most patients were pT1-2 stage. Yolk sac tumor was present in 75%, while 16% had embryonal carcinoma, and 9% had choriocarcinoma. When evaluable, lymphovascular invasion (LVI) was present in 36/66 (55%) of patients. Over a median follow-up of 5.0 years, no patients died and 24 patients (27%) relapsed (median relapse-free survival not reached). Predictors of relapse included presence of choriocarcinoma (HR 4.3, p=0.004), embryonal carcinoma (HR 3.8, p=0.002), pT3 stage (HR 6.9, p=0.027), and age >12 years (HR 3.1, p=0.011). LVI (HR 2.4, p=0.072), serum tumor markers, and dominant tumor size did not reach significance. Pediatric CS I GCT patients exhibit remarkable 5-year survival. Conclusions: Using combined data from multiple prospective trials, our study identifies clinicopathologic features that predict relapse and potentially inform personalized treatment for these patients.