The clinical and pathologic features of 70 juvenile granulosa cell tumors (JGCTs) of the testis are presented. The patients were from 30 weeks gestational age to 10 years old; 60 of 67 (90%) whose ages are known to us were 6 months old or younger. Sixty-two underwent gonadectomy, 6 wedge excision, and 2 only biopsy. Twenty-six tumors were left sided and 22 right sided. Six occurred in an undescended testis and 2 in dysgenetic gonads. The most common presentation was a testicular mass (65%), followed by an "enlarging testis" (25%). Six of 14 patients in whom it was measured had "elevated" serum α-fetoprotein (AFP), likely physiologically, and 1 had gynecomastia. The tumors measured 0.5 to 5 cm (mean, 1.7 cm; median, 1.5 cm) and were most commonly well circumscribed and typically yellow-tan; approximately 2/3 had a cystic component, whereas 1/3 were entirely solid. Microscopic examination typically showed a lobular growth, punctuated in 67 cases by variably sized and shaped follicles containing material that was basophilic (21%), eosinophilic (44%), or of both characters (35%); 3 lacked follicles. In nonfollicular areas, the tumor cells typically grew diffusely but occasionally had a corded arrangement (26%) or reticular appearance (29%). The stroma was either fibrous or fibromyxoid; hemorrhage associated with hemosiderin-laden macrophages was focally seen in 16%. The tumor cells were mostly small to medium sized with round to oval nuclei containing inconspicuous nucleoli and moderate to abundant, but occasionally scant, pale to lightly eosinophilic, sometimes vacuolated, cytoplasm; nuclear grooves were infrequent (6%). Focal columnar morphology was seen in 27% of the tumors. Mitoses were plentiful in 37%, and apoptosis was prominent in 46%. Intratubular tumor was seen in 43% and entrapped seminiferous tubules in 70%. Lymphovascular invasion was present in 2 cases, rete testis involvement in 4, and necrosis in 1. Rare features/patterns included: regressed tumor with hyalinization and prominent blood vessels (13%), papillary growth (4%), basaloid morphology (1%), spindle cell predominance (1%), microcystic foci (1%), adult granulosa cell-like (1%) patterns, and hyaline globules (1%). Inhibin (16/18), calretinin (8/9), WT1 (6/7), FOXL2 (12/12), SF-1 (12/12), and SOX9 (6/11) were positive, whereas SALL4 and glypican-3 were consistently negative in the neoplastic granulosa cells. Only 1 of 10 tumors was focally positive for α-fetoprotein. JGCT is a rare neoplasm with a wide morphologic spectrum that also occurs rarely in undescended testes and dysgenetic gonads. The solid and reticular patterns may pose diagnostic challenges, but the lobular appearance and follicular differentiation are characteristic. Immunohistochemical stains may aid in its distinction from other tumors of young male individuals, particularly yolk sac tumor, a neoplasm that peaks at a somewhat later age. Twenty-four patients with follow-up, including 4 of 6 patients treated with wedge resection/biopsy, had no evidence of disease (2 to 348 mo; mean, 83 mo; median, 61 mo). One additional patient was alive at 260 months, but the disease status is unknown. The benign clinical course of all cases of JGCT with follow-up, despite often frequent mitotic activity, supports testis sparing surgery when technically feasible.