We have studied 32 unrelated families with a site-specific reciprocal translocation between chromosomes 11 and 22 [t(11;22) (q23;q11)]. In translocation heterozygotes 3:1 meiotic segregation occurs and results in abnormal progeny who carry the der(22) as a supernumerary chromosome. Phenotypic findings consistent with 47,XX (or XY), +der(22), t(11;22) include mental retardation, preauricular skin tag and/or sinus, ear anomaly, palate anomaly, micrognathia, congenital heart disease, and genital anomalies in males. The frequency of abortions among offspring of male and female heterozygotes is increased. Segregation analysis shows that the risk of unbalanced offspring to be born to female heterozygotes may be as high as 10%, and that there may be a significant risk to male heterozygotes as well. The overall carrier frequency among progeny of 11;22 translocation carriers is 70.6%. The occurrence of multiple 11;22 translocation events is supported by de novo occurrence of translocation, familial heteromorphic variants of the der(22), and varied racial and ethnic backgrounds of the families. To our knowledge, with the exclusion of centric fusion translocations, this represents the only example of nonrandom exchange in a constitutional chromosomal rearrangement.