[Contribution on the familial occurrence of malignant testicular tumors].

Eight cases of testis tumors in monozygote twin brothers are described in the bibliography. One case is added here. Nearly at the same age, two twin brothers got a right side embryonal teratocarcinoma. The histories of diseases were approximately identical. The brothers died two years later. The possibility of genetic factors causing or influencing the development of malignant testicular tumors are briefly discussed.