A developmentally retarded 21/2 year old male with seizures and spasticity has been found to carry only the larger product of a reciprocal translocation between the long arms of No. 18 and a 13–15 group chromosome. The absence of a smaller reciprocal of the translocation suggests that the deletions of the two involved chromosomes are the cause of the phenotypic abnormalities. The report includes dermatoglyphic analysis and blood groups, haptoglobins, Gc types and transferrins of the child and his parent