The present authors report an autopsy case of a malformed male newborn with de novo duplication of the distal part of the long arm of chromosome 14 (14q24.1 to 14qter) in this paper. The partial trisomy of 14q was due to the unbalanced translocation at the end of the satellite stalk of chromosome 14. This autopsy case also had many kinds of external malformations including odd skull and facies, narrow thorax, and prominent calcaneus as well as retentio testis. The autopsy examination revealed aplasia of the thymus and marked hypoplasia of systemic lymphoid tissues. During an immunohistochemical study of the lymphoid tissues the population of T cells showed only a minority of lymphocytes. While several cases of distal trisomy 14q with cardiac malformations or a developmental abnormality of the thymus and the parathyroids seen in the third and fourth pouch defects have been reported previously, the present case was the first of this syndrome with aplasia of the thymus and systemic lymphoid hypoplasia.