A case is presented in which monosomy 21 was detected by routine cytogenetics and fluorescence in situ hybridization (FISH) studies demonstrated an unbalanced translocation t(5;21). The patient was partially monosomic for both 5p and 21q. The phenotype of the infant showed some features of the 5p- (cri-du-chat) syndrome, but there were also features present which were uncharacteristic of this syndrome. The present findings, combined with similar cases reported in the literature, provide further support for a proximal monosomy 21q syndrome.