The present report concerns the clinical and cytogenetic findings in a liveborn girl with trisomy for the long arm of chromosome 20. She was the unbalanced product of a maternal t(18;20)(q23.2;q13.1) translocation. Our case is compared to the 3 previous reports of trisomy 20q associated with telomeric translocation. Adenosine deaminase dosage falls in the normal range and confirms the exclusion of the ADA locus from the region extending distally to 20q13.1.