Two sibs show a strikingly concordant syndrome of congenital anomalies and G-banding reveals that each has partial trisomy 20p resulting from a t(18;20) translocation. They resemble other cases of partial trisomy 20p in some respects but also differ in some ways. Their normal sib, mother, and half-aunt are balanced heterozygotes for the t(18;20) translocation. The segregation of the balanced translocation in this family is associated with an extremely poor reproductive record. The segregation pattern closely parallels that of a t(13;20) translocation in a family described by Carrel et al. (1971) and Francke (1972). The similarity of segregation patterns is predictable on the basis of probable pachytene configurations, but the dissimilarity of phenotypes between families is not readily explained.