CD5 is a transmembrane glycoprotein on all T cells and on a subpopulation of B cells. Based on the analysis of chicken CD5-cDNA we have previously shown that the structure of the CD5 protein is conserved between species. Here we report the isolation and chromosomal mapping of the chicken CD5 gene. The gene spans 3.4 kb and is extremely compact with a high GC-nucleotide content. There are 10 exons and the introns are spliced out similarly to those in the human CD5 gene. Each of the three extracellular scavenger receptor cysteine-rich (SRCR) domains is encoded as an exon of its own, as is the proline-rich hinge region that separates the first two membrane-distal SRCR domains. The fluorescence in situ hybridization (FISH) technique was used to map the gene to chromosome five. This is the first report describing the organization of the CD5 gene from a nonmammalian species.