We describe a case of tertiary trisomy (22q11q) 47,XX,+der(22),(22pter = to 22q13 :: 11q25 = to 11qter) in a child with mental retardation, cleft palate, and congenital heart disease resulting from 3 : 1 meiotic nondisjunction in a maternal (11;22) translocation carrier. The clinical findings in previously reported cases are reviewed and compared with the features of reported patients with "partial trisomy 11q" and "trisomy 22" syndromes. Half of the ten reported families had additional balanced translocation carriers who may have an increased risk of having a liveborn child with an MCA/MR syndrome, although none have been reported to date.