Recombinant 8 syndrome is a well-established syndrome with mental and developmental retardation and usually severe cardiac anomalies. A carrier parent will produce affected offspring in 6% of pregnancies and carrier offspring in 53% of such pregnancies. Four New Mexican kindres ascertained by the discovery of four apparently unrelated probands with cytogenetically confirmed recombinant 8 syndrome were studied. We found that (1) recombinant 8 syndrome will soon no longer be confined to New Mexico and southern Colorado, (2) the number of persons at risk may be higher than previously considered, and (3) through proper pedigree techniques and increased professional education, most carriers can be identified.