We report 33 pure yolk sac tumors of the testis from boys 5 to 71 months of age (mean 20.7 mo) diagnosed from 1918 to 2014. All except 1 underwent orchiectomy, with lymph node dissections (all negative) performed in 18; 21 also received chemotherapy and 12 radiotherapy. The tumors were 1.6 to 7.0 cm (mean 3.7 cm) and were nonencapsulated, with a gray to yellow, often mucoid, cut surface. The commonest pattern was reticular-microcystic, but macrocystic, papillary, endodermal sinus (Schiller-Duval bodies), labyrinthine, myxomatous, glandular, and solid patterns were also observed. Follow-up was available for 32 patients (mean 100.5 mo; range, 3 to 456 mo). Twenty-four patients (including 4 who did not receive adjuvant therapy) were without evidence of disease, 8 had metastatic disease; 5 of the latter died of tumor and 1 of treatment complications. Two patients with metastasis were cured with radiation with or without chemotherapy. Two or more of the following were associated with a poor outcome in patients presenting with stage I cases: tumor size >4.5 cm (4/6 tumors [67%]), invasion of rete testis and/or epididymis (3/7 tumors [43%]), and necrosis (6/17 tumors [35%]). In the nonmetastasizing group, 2 or more unfavorable features occurred in only 3/24 tumors (13%) (P=0.0001). It is crucial that this tumor be distinguished from the juvenile granulosa cell tumor, which occurs at a slightly younger age and has distinctive features, although there may be some morphologic overlap. The survival of young boys with testicular yolk sac tumor is very good because of both effective chemotherapy and likely, the inherent characteristics of the tumor in this age group.