A boy with multiple congenital anomalies was found to have a small extra chromosome. This small chromosome was interpreted as a der(22)mat because his mother was a balanced carrier with 46,XX,t(17;22) (p1;q1) chromosomes. It is hoped that with the use of the banding techniques many karyotypes will be revaluated and reinterpreted. The mother's karyotype was erroneously interpreted earlier as a 21/22 translocation.