An infant with trisomy 9pter yields 9q22 resulting from 3:1 segregation in a 46,XX t(1;9) (p36;q22) mother.

A newborn infant with a 47,XY,+ der(.),t(1;9) (p36;q22)mat chromosome complement and the clinical features of the 9p trisomy is described. A review of the reproductive histories of five cases with trisomy 9pter yields 9q21 or 22 indicate that the balanced translocation mothers of these infants may have as high as a 23% chance of producing a chromosomally unbalanced offspring due to 3:1 disjunction.