Graham DA, Jewitt MM, Fitzgerald PH. Trisomy 18 mosaicism with complete peripheral lymphocyte trisomy and normal intelligence. Clin Genet 1992:41: 36–38.We report a patient with trisomy 18 in all peripheral lymphocytes, mosaicism in cultured fibroblasts, mild nonspecific dysmorphic features, and normal intelligence. Trisomy 18 mosaicism with complete peripheral lymphocytic trisomy has not been previously described. The karyotype of lymphocytes is not diagnostic in the absence of congruent morphologic feature