Histological pleomorphism of testicular germ cell tumors complicates diagnosis. These tumors share highly specific differentiation properties ranging from intra-tubular neoplasia to classical infiltrating lesions. This general review presents the histopathological features and diagnostic criteria of typical forms and atypical variants. In current practice, distinction between seminoma and non-seminomatous germ cell tumors is fundamental for treatment. Histological typing of non-seminomatous tumors may be problematical, especially in "mixed" forms. Vitelline tumor variants and atypical embryonic carcinoma are described. Unlike scattered isolated syncytiotrophoblastic cells, true chorio-carcinoma is rare and must be carefully identified. Such cells are frequently associated with seminoma, embryonic carcinoma and vitelline tumors. Intra-tubular germ-cell neoplasia and gonadoblastoma, are pre-invasive lesions associated with cryptorchidism and gonadal dysgenesis. Teratomatous elements usually occur in mixed germ cell tumors. Rare pure teratoma are benign in children. On the contrary, post-pubertal forms have an unpredictable evolution.