Gonadal stromal tumors generally are benign and hormonally silent. When hormonally active, they may cause either virilization or feminization, posing an endocrine threat to the prepubertal boy. Accurate diagnosis is essential to differentiate those tumors that require medical management from those best treated by surgical ablation and to distinguish the benign ones from the malignant. Leukemic infiltration is the most common secondary testis tumor; others are neuroblastoma, Wilms' tumor, and gonadoblastoma.