A newborn infant with multiple congenital anomalies was diagnosed with an unbalanced translocation of chromosomes 1 and 5. Studies of parental chromosomes revealed a complex rearrangement in the patient's mother involving the exchange of terminal long arms between chromosomes 1 and 5 and the insertion of an interstitial segment from the same chromosome 5q into chromosome 2q by high-resolution G-banding. Further study of the mother's chromosomes by fluorescent in situ hybridization (FISH) detected an additional insertion between the rearranged chromosomes 2 and 5, which was not revealed by G-banding. This led to the identification of a complex translocation-insertion between 3 chromosomes with at least 5 breaks [t(1;5;2)(1pter--> 1q42.3::5q23.2-->5qter;5pter-->5q21.2:: 2q33--> 2q35::1q42.3-->1qter;2pter-->2q33::5q21 .2--> 5q23.2::2q35-->2qter)] and illustrates the value of FISH as an adjunct to standard cytogenetics, particularly in cases of complex rearrangements.